.

1

Data from the

NATIONAL SURVEY OF FAMILY GROWTH

ContraceptiveEfficacy

AmongMarried Women

Aged 15-44 Years

Un”wstates

Statistics are presented on the effectiveness of contraceptives used

by married women aged 15-44 years. The percent of women who

failed to prevent an unwanted pregnancy or to delay a wanted

pregnancy until its desired time is shown for various demographic

and socioeconomic groups.

DHHS Publication No. (PHS) 80-1981

Series 23

Number 5

US. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Office of Health Research, Statistics, and Technology

National Center for Health Statistics

Hyattsville, Md. May 1980
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J

NATIONAL CENTER FOR HEALTH STATISTICS

DOROTHY P. RICE, Director

ROBERT A. ISRAEL, Deputy Director

JACOB J. FELDMAN, Ph.D., Associate Director for Analysis

GAIL F. FISHER, Ph.D., Associate Director for the Cooperative Health Statistics System

ROBERT A. ISRAEL, Acting Associate Director for Data Systems

ALVAN O. ZARATE, Ph.D., Acting Associate Director for International Statistics

ROBERT C. HUBER, Associate Director for Management

MONROE G. SIRKEN, Ph.D., Assoctite Director for MathematicalStatistics

PETER L. HURLEY, Associate Director for Operations

JAMES M. ROBEY, Ph.D., Associate Director for ProgramDevelopment

GEORGE A. SCHNACK,Acting Associate Director for Research

ALICE HAYWOOD,Information Officer

DIVISION OF VITAL STATISTICS

JOHN E. PATTERSON, Director

ALICE M. HETZEL, Deputy Director

WILLIAM F. PRATT, Ph.D., Chie~ Family Growth Survey Branch

MABEL G. SMITH, chie~ Statistical Resources Branch

JOSEPH D. FARRELL, Chief ProgrammingBranch

Vital and Health Statistics-Series 23-No, 5

DHHS Publication No. (PHS) 80-1981

Libra~ of CongressCatalog CardNumber 79-22370
FOREWORD

The National Survey of Family Growth collects information on the fertility,

family planning practices, and reproductive health of women in the United States.

The information is based on standardized home interviews with large, nationally

representative samples of women in the reproductive years.

To supplement its own analyses of the Survey’s rich data, the National Center

for Health Statistics caIIed upon various specialists outside the Center to prepare

several analytical reports in the series of Vital and Health Statistics.

This report was pkirmed by Ms. Barbara Vaughan, Dr. James TrusselI, Dr. Jane

Menken, and Dr. EliseJones of the Office of Population Research, Princeton Uni-

,.

versity, within a general framework requested by the National Center for Health

Statistics. These authors conducted the analysis and prepared a report to the

Center on their findings. Table A, all estimates of standard errors, and appendixes

I and II were prepared by Center staff, under the supervision of William Grady,

who also adapted the report for publication in Vital and Health Statistics.

The report presents a detaiIed analysis and a complete methodological discussion of measures of contraceptive effectiveness derived by Iife-table techniques,

selected highlights of which have been pubIished previously. Although the data

from which these measures were computed refer to contraceptive experience in

the early 1970’s, they are unique and of continuing current importance for any

authoritative discussions of contraceptive efficacy. These data are the first to incIude monthly information for a 3-year period on both contraceptive use and

exposure to sexual intercourse, making possible the most refined life-table

measures of contraceptive efficacy so far available for a nationally representative

sample of American women. They replace other measures, still frequently cited,

which are based on outdated methods (e.g., the Pearl index) and upon noncomparable studies from different cultures, many of which were conducted weI1before the 1970’s. The rates in this report undoubtedly provide an important

baseline against which findings from many future studies of contraceptive efficacy

wiIl be compared.

The authors are indebted to Dr. Norman Ryder of the Office of Population

Research, Princeton University, for his helpful criticisms of earlier versions of this

report.

William F. Pratt, Chief

Family Growth Survey Branch

Division of Vital Statistics

...

Ill
CONTENTS

Foreword ....................... .........................................................................................................................

Introduction ............................................ .................................... ...........................................................

Summary of Principzd Findings ...................................................................................................... ........

Measures of Contraceptive Effectiveness ................................................................................................

Source and Limitations of the Data .......................................................................................................

Data Source ........................................... ...........................................................................................

Description of Sample ........ ...................................................................... ..................... ....................

Identifying the Outcome of Each Contraceptive Use Intervsd ....... ...................................... .......... ....

Contraceptive Failure in the First Year of Use .................................. .....................................................

Contraceptive Intention: Prevent Versus Delay ................................................................................

Age, Education, and Parity ................................................................ ..................................... ..........

Relative Age .. .......................................... ...... ....................................................................................

Method of Contraception ............ ...... ...............................................................................................

Race .............................. ...................................................... ................ ................................ ..............

Religion ............................................. ...... .. .......................... ................................ ........................... ...

Marriage Cohort ..................... ...... .. .......................................... .........................................................

Place of Residence ............................................................................................................................

Failure Rates at H;gher Durations ........................... ................................. ..............................................

Extended Use Effectiveness ..... ...................................................... .......... ...................... .......... ...............

Continuation Wtes .................................. ..................................... ..........................................................

The Relationship Between Extended Use Effectiveness, Use Effectiveness, and Continuation Rates .....

References .............. .................. .......... ................................ ....................................................................

Lkt of Detailed Tables ........................................................... ........................................ ........................

Armendixes .-

1.

IL

111.

N.

v.

VI.

VII.

Technical Notes ......................................... .......................................................... .....................

Definition of Terms ..................................................................................................................

Selection of Sample ........................................................ ...... .......... ...... ....................................

The Calculation of Gross Rates of Continuation for Contraceptive Methods: Single

and Multiple Increment Life Tables ........................................................... ...............................

Summay of Pertinent Portions of the NSFGQuestionnaire .....................................................

Classification of Contraceptive Use Intervals by Contraceptive Intention .................................

Contraceptive Failure Rates bv Relative Age. Contraceptive Intention. Aee at

1.

2.

Last Liv~Birth, Education, m’d Parity - ‘ “

,-

......................................................................................

LIST OF TEXT FIGURES

Percent of married women 15-44 years of age attempting to prevent an unwanted pregnancy who

experienced a contraceptive failure during the first year of use (for users of all contraceptive

methods except steriliiation), by age at last live birth: United States, 1970-73 .................................

Percent of married women 15-44 years of age who experienced a contraceptive failure during the

first year of use (for users of all contraceptive methods except sterilization), by contraceptive

intention and education: United States, 1970-73 ......................... .......... ..........................................

...

111

1

1

3

4

4

5

i’

8

8

9

10

11

12

14

14

15

15

16

17

18

20

21

38

43

46

49

58

60

62

9

9

iv
3.

4.

5.

6.

7.

A.

B.

c.

Percent of manied women 15-44 years of age attempting to prevent -anunwanted pregnancy who

experienced a contraceptive failure during the first year of use (for users of all contraceptive

methods except sterilization), by parity: United States, 1970-73 .....................................................

Percent of married women 15-44 years of age who experienced a contraceptive failure during the

first year of use, by contraceptive intention and contraceptive method: United States, 1970-73 .....

Percent of married women 15-44 years of age who experienced a contraceptive failure during the

first year of use (for users of alf contraceptive methods except sterilization), by contraceptive intention and race: United States, 1970-73 .........................................................................................

Percent of married white women 1544 years of age who experienced a contraceptive failure

during the first year of use (for users of all contraceptive methods except sterilbration), by contraceptive intention and religion: United States, 1970-73 .....................................................................

Percent of married women 15-44 years of age who experienced a contraceptive faifure during the

firstand second years of use (for users of all contraceptive methods except sterilksation), by contraceptive intention: United States, 1970-73 ....................................................................................

LIST OF TEXT TABLES

Number of ever-married women 15-44 vears of aee who had at least one intervaf of entirely marital

contraceptive use between July 1, 1970 and Jul~ 1, 1973 (applicable population) and th~ number

of women from that population whose information was sufficient to be included in this study

(study population) by race, and percent distribution by religion, education, geo~aphic region, and

place of residence: United States, 1973 ............................................................................................

Quartile upper age limit for ever-married women 15-44 yeans of age, by birth order and quartik

United States, 1973 ................................................................................................................. ........

Percent, standardized by contraceptive intention, of married women 1544 years of age who

experienced a contraceptive fake during the- first year of use, by conkceptive ðod:

United States, 1970.73 .....................................................................................................................

D. Percent of months of exposure to the risks of conception during the first year of contraceptive

E.

use for women whose intention was to prevent an unwanted p&nancy, during which tht pill,

IUD, or sterilization were used, and during which the IUD was used, by relative age and race:

United States, 1970.73 .....................................................................................................................

Estimates of components of extended use effectiveness rates for married women 1544 years of

age, by contraceptive intention and race: United States, 1970.73 ....................................................

SYMBOLS

Data not available—--—-—— -—-—— -- -

Category not applicable --------------- . . .

Quantity zero--–---—— ------------------ -

Quantity more than O but less than 0.05—- 0.0

I

Figu~e does not meet standards of

reliability y or precision—————————— *. I

10

11

13

14

16

6

11

12

13

19

I J

v
CONTRACEPTIVE EFFICACY

AMONG MARRIED WOMEN

AGED 15-44 YEARS

Barbara Vaughan; James Trussell, Ph.D.;Jane Menken, Ph.D.;

Elise F. Jones, Ph.D., Office of Population Research, Princeton University,

and William Grady, M.A., Division of Vital Statistics

INTRODUCTION

This report contains an analysis of the continuity and effectiveness of contraceptive practice among married women aged 15-44 years in

the United States during the 3-year period July

1, 1970 through July 1, 1973. The analysis is

based on data from cycle I of the National Survey of Family Growth, conducted by the National Center for Health Statistics. The National

Survey of Family Growth was designed to provide information about fertility, family planning

intentions and activity, and other aspects of

maternal and child health that are closely related

to childbearing. Data were collected through

personal interviews with 9,797 women aged

15-44 years who either had ever been married or

had offspring living in the household. Interviews

were conducted between July 1973 and February 1974, and centered on September 1973.

Respondents were seIected from a multistage,

area probability, cross-sectional sample of households in the conterminous United States. The

statistics reported here do not pertain to all

contraceptors, but to women who were both

married and using contraceptives for some time

during the 3-year study period. Appendix I contains information about the sample design, data

collection, and estimating procedures. Appendix II contains definitions of certain terms used

in this report, and appendix III describes in detail the procedures used in selecting cases for

this study.

SUMMARY OF PRINCIPAL FINDINGS

The contraceptive failure rates presented

here are the first to be produced using a new

technique to determine rates for a nationally

representative sample of women. With this technique, improved estimates of the percent of

women who experienced a contraceptive failure

during 1 year of continuous use are obtainable.

The failure rates for specific methods of contraception are of fundamental value in evaluating

each method and in providing guidance to

clinical patients in the selection of a method.

Comparisons of failure rates by socizd and demographic characteristics such as age, parity, race,

and education provide insights into the causes of

group differences in both unwanted and completed fertility.

Wit&n one year after the initiation of contraceptive use, about 4 percent of a sarnple of

married women aged 15-44 years in the United

States who wanted no addkional chiidren at any

time in the future became pregnant. Among

women who sought to delay a wanted pregnancy, the contraceptive failure rate was about

7 percent. Because the failure rate of preventers

is significantly Iower than that of delayers, and

because the motivation for using contraceptives

is so different, failure rates were calculated

separately for the two groups of women.

Among women attempting to prevent an

unwanted pregnancy, the first-year failure rates

by individual contraceptive method ranged from

1
a low of no failures for women employing sterilization, to a high of about 13 percent for users of

foam, cream, and jelly. Between these extremes,

the contraceptive failure rates were about 2 percent for oral contraceptive (the pill), about

3 percent for the intrauterine contraceptive device (IUD), about 7 percent for the condom, and

about 10 percent for the diaphragm and for the

rhythm method. Among delayers, the first-year

contraceptive failure rates were lowest for the

pill (about 2 percent). and highest for the

rhythm method (about 29 percent). Failure

rates for the other devices were as follows:

about 6 percent for the IUD; about 14 percent

for the condom; about 16 percent for the diaphragm; and about 17 percent for foams,

creams, and jellies.

Among the respondents who were attempting to prevent any additional births, first-year

failure rates were found to decrease with increasing age at last live birth, educational attainment,

and parity. Women 15-19 years of age at the

time of the last live birth had a failure rate of

about 7“percent; for those 35-39 years of age the

rate was about 1 percent. For women with less

than 12 years of education the first-year failure

rate was about 4 percent, and for those with

more than 12 years the rate was about 3 percent. The failure rates associated with parity

(number of children ever born) ranged from a

high of about 5 percent for women with no

children to a low of about 2 percent for women

with 5 children. The only major exception to

the pattern of declining failure rates with increasing parity occurred among women with six

or more children: they experienced a contraceptive failure rate of about 4 percent during

the first year of use.

There was no systematic relationship between age at last live birth or parity and firstyear contraceptive failure rates among sample

women who were attempting to delay the birth

of a wanted child. However, education was

found to be related to failure: about 9 percent

of women with less than 12 years of education

and about 7 percent of those with more than

12 years experienced a contraceptive failure.

There was little difference in the proportions

of black and white women who failed to prevent

an unwanted pregnancy during the first year of

contraceptive use. However, the failure rate of ‘

women attempting to delay a wanted pregnancy

was 3 percentage points higher for white women

than for black women, who had a failure rate of

about 4 percent.

Among white women in the sample, Catholic

women who sought to prevent an unwanted

pregnancy were slightly more successful than all

other women; about 3 percent compared with

4 percent, respectively, had first-year failures.

However, among white women who sought to

delay a wanted pregnancy, Catholic wornen were

slightly less successful; about 9 percent failed,

compared to about 7 percent of other women.

Second-year failure rates were found to be

generally lower than first-year rates. About

2 percent of the women attempting to prevent

an unwanted pregnancy and 5 percent of the

women attempting to delay a wanted pregnancy

experienced a contraceptive failure during the

second year of use. These figures are about

2 percentage points below the corresponding

first-year rates.

When extended ‘use-failure rates (a measure

which combines effectiveness of method use

with continuation of use) were analyzed, it was

found that black women were more likely than

white women to fail to prevent an unwanted

pregnancy. The higher extended use-failure rates

occur primarily because black women, although

more likely than white women to use the most

effective contraceptive methods, are more likely

to discontinue use of a method without substituting another. Although the difference in continuation between black and white women is not

large, even a small difference qeatly increases

the probability of a pregnancy for the group

that started using a method.

Low failure rates are found consistently

throughout this study. Considerably higher rates

were reported by Ryderl in the only previous

study representative of all currently married

women in the United States. Although the differences are largely methodological (he used extended use effectiveness), they also reflect a

genuine improvement in effectiveness over time

and a switch to more effective methods. Overall,

the low use-effectiveness failure rates lmaskthe

not insignificant proportion of women who, for

one reason or another, abandoned use clf contra2
ceptives altogether. In this study, about 3 percent and about 10 percent of those whose intentions were to prevent and delay, respectively,

terminated use of a contraceptive method within

1 year without switching to another. For these

women there is a high probability of unintended

pregnancy.

Another consistent finding reported here is

that within relative age and contraceptive intention categories, there is little variation in failure

rates by religion, race, marriage cohort, or education. There is some variation, but not nearly

the range reported by Ryder. 1 There seems to

have been a convergence in efficacy among subdivisions of the population which exhibited

sizable differentials in earlier studies (based on

information from before 197 O). The convergence among education, religious, and racial

groups may be a function of the vast increase in

the quantity and quality of contraceptive information disseminated, and of the increased activity in family planning programs over the last

decade. This convergence in failure rates also

reflects the coitus-independent property of the

newer, most effective methods of contraception.

No coitus-related action need be taken when

using sterilization, the pill, or the IUD. In contrast to the use of the condom, foam, diaphragm, rhythm, or withdrawal, the effective

use of these three methods does not require high

motivation. Both the effectiveness of sterilization, the pill, and the IUD and the fact that

70 percent of all the months of contraceptive

use included in this analysis were contributed by

women using these three methods provide sufficient proof of a contraceptive revolution.

MEASURES OF CONTRACEPTIVE

EFFECTIVENESS

In previous studies designed to be representative of the entire ever-mamied U.S. population,

data sufficient to estimate contraceptive use and

failures on a month-by-month basis were not recorded. Therefore, for computing effectiveness

rates, a measure known as “extended use effectiveness” was employ ed.z~$ For this measure,

the period of exposure to the risk of conception

is assumed to include the entire interval between

pregnancies (minus months of separation from

the spouse) if contraceptives were used at any

time during that interval. Further, an unintended pregnancy that occurred during the interval is assumed to be a contraceptive failure, even

if the method of contraception was abandoned

before the pregnancy occurred.

The extended use-effectiveness measure is

readily calculable when periods of contraceptive

use cannot be separated from periods of nonuse.

When such a separation can be made, the use of

this measure is a matter of judgment. Some investigators feel that the true measure of, the

effectiveness of a contraceptive method should

include the method’s attractiveness or loyalty of

use, and would therefore choose to calculate

extended-use effectiveness.

An alternative procedure possible when

months of contraceptive use can be separated

from months of nonuse is the calculation of two

measures. One measure is the effectiveness of a

contraceptive method when it is used; the second is the continuation rate—the proportion of

women who are still using a method after various durations of time. Because the 1973 National Survey of Family Growth included a

3-year, month-by-month retrospective record of

contraceptive use and nonuse, both continuation

and effectiveness measures can be calculated.

However, it is important to note that these

measures are calculated on the assumption that

among women included in the subsequent

analysis, reporting is correct. Misstatements of

periods of use and the timing of pregnancy will,

of course, be reflected in the estimated failure

rates.

The preferred methodology in estimating

contraceptive use effectiveness or continuation

of use involves constructing a life table. A detailed description of the procedure is given in

appendix IV, but a brief description is warranted

here. A life table for measuring continuation

rates can be regarded as a table listing, for each

duration since the initiation of use of a contraceptive method, the proportion of women who

are still using that contraceptive. Such a table is

a “multiple decrement” life table since there are

many ways to exit from it. Women may become

unintentionally pregnant or may stop using contraceptives to become pregnant or for medical or

3
other reasons. Each reason for stopping competes with every other reason, and the continuation rate measures the net effect of all reasons

acting simultaneously, When measuring contraceptive effectiveness, the goal is to eliminate the

effects of all reasons except becoming pregnant

unintentionally. It is possible to construct an

associated “single decrement” life table which

shows, when all reasons for stopping use other

than unintentional pregnancy have been eliminated, and for various durations since the initiation of contraceptive use, the proportion of

women who have not experienced a contraceptive failure. For a given duration, say 12 months,

the proportion of women who have stopped

using a method for all reasons combined cannot

be smaller than the proportion of women who

have experienced a contraceptive failure.

In clinical trials, it is usually possible to observe each woman from the initiation of contraceptive use. However, in a cross-sectional study

such as the National Survey of Family Growth,

the proportion of women who initiate use

(either for the first time or after a period of

nonuse) within the period covered by the

month-by-month chart of contraceptive use (in

this case, 3 years) is small compared with the

total number of users. In addition, no continuation or failure rates for more than 3 years could

be calculated if only the data for women who

initiated contraceptive use during the observation period were considered, Increasing the

period covered by the month-by-month chart

would solve the problem, but it is clem that a

retrospective account of contraceptive utilization becomes less accurate as the period of time

covered increases. The designers of the National

Survey of Family Growth therefore chose the

3,year period as a compromise between the goals

of collecting as much information as possible

and minimizing recall error.

The construction of a multiple increment

life table provides a way to utilize the full range

of experience recorded for individual women

within the 3-year period. It is assumed that a

woman who, at the start of the 3-year period is

in, say, her 6th month of use, is representative

of all women who enter their 6th month. Therefore, her experience from the 6th month on is

included in the life table. Her experience before

the 6th month is not included, since the experience of women who started use at the same time

but terminated for any reason before the 6th

month cannot be observed or retrieved.

If there are strong trends in continuation or

effectiveness rates over time, the multiple increment life table based on period rates gives a

biased estimate of the failure rates at longer

durations for any cohort of women initiating a

segment of contraceptive use during the period

in question. Since the focus here is 12-month

failure rates, this consideration is unlikely to be

important.

SOURCE AND LIMITATIONS

OF THE DATA

Data Source

The data collected in the 1973 National

Survey of Family Growth (NSFG) and available

for a life-table analysis of contraceptive use included: dates of the respondent’s current marriage and all previous marriages and ~marriage

dissolutions; information about fecundity, current reproductive intention, number of pregnancies and live births, dates of all conceptions

and pregnancy terminations, and the 3-year

chart of monthly contraceptive status. The latter

contains one code for each calendar month between July 1, 1970 and the date of the interview. Possible codes are pregnancy, -contraceptive method used (a separate code for each of 18

possible methods), no intercourse, and no contraceptive method used. Coding priority was in

the above order for months in which more than

one code might be appropriate. If two methods

were used simultaneously, priority was given to

the method assumed to be more effective. If

methods were changed during the month, priority was given to the method used in the

previous month.

Information pertaining to each of the respondent’s pregnant y intervals that began or

ended in or covered the study period including

the interval following the most recent pregnancy (the open interval) was also collected. It

included data on reproductive intentions,. the

respondent’s feelings at the time of conception

4
about the timing of the pregnancy (too soon,

too late, or right time),a and, if contraception

was used during the interval, dates use started

and ended and whether use was stopped before

conception occurred. Appendix V gives a summary of the interview question sequence and

wording for questions essential to the definition

of key “variables.

Several possible sources of ambiguity arise in

these data. First, since the 3-year chart contains

onIy one code for each month, the circumstances of transition from one code to another

cannot be adequately represented. For instance,

a month in which contraceptives were used followed by a month in ,which a pregnancy

occurred could represent contraceptive use that

(1) ended in the month prior to conception,

(2) ended in the month of conception, or

(3) continued for several more months, until the

woman realized she was pregnant. The pregnancy interval data, which contain dates of

starting and stopping contraceptive use and the

date of conception, are inadequate in other

respects. Only the total numbers of months in

which no intercourse occurred, and not the

dates of no exposure, are shown. Information

about sterilization is included only if a respondent volunteered such information.

A second source of ambiguity results from

the process of imputing values for data missing

because an answer was not given, not ascertained, or in some cases unknown. Missing data

were imputed separately for the 3-year chart and

the pregnancy interval questions. When imputation was based on independent information for

the same respondent, the resulting data for that

respondent were consistent. However, most imputations were made using known information

from other respondents who were matched by

age, race, and so forth, either by randondy selecting known values for respondents with the

same matching criteria or by sorting the respondents on the matching criteria and using

aThese data were used to determine whether or not

the intention in using contraceptives was to delay

another wanted pregnancy or to prevent any further

(unwanted) pregnancies. This dichotomous intention

variable proved to be very powerful and is discussed

more fully in a later section.

known values from the adjacent record. These

procedures sometimes resulted in the imputation

of information that was not consistent with

information known about the respondent.

Description of Sample

To calculate the use effectiveness of contraceptives, consideration was limited to those

pregnancy intervals in which contraceptive

faiIure was possible, during the observation

period (July 1, 1970-JLdy 1, 1973), that is, in

which a woman was sexually active and using

contraceptives. Although direct information on

sexual activity was not obtained, it was assumed

for the study that married women were engaged

in regular sexual activity and that unmarried

women (single, widowed, divorced, or separated)

were not; thus women who were unmarried

throughout the observation period were excluded from the study, and some intervals of

contraceptive use for the remaining women were

exclud,ed because the women were unmarried at

the beginning of the interval. Women who were

sterile (or who had sterile husbands) throughout

the observation period because of an accident,

illness, or therapeutic operation were also excluded under the assumption that they did not

practice contraception. Finally, all other intervals in which no use of contraceptives was

reported were excluded from consideration.

After the exclusions, the sample included

women who had one or more intervals of em

tirely marital contraceptive use which began in

the observation period, or which began before

but continued into the observation period. It

represented about 23 million women in the U.S.

population in 1973, as estimated by NSFG;

some of the characteristics of this population are

shown in table A under the headings “applicable

population.” These women make up the population for which contraceptive failure (as operationally defined with the data available) was possible during the observation period, and the

population to which the results of this study are

intended to apply. It is not, however, the popu.

lation whose experience was actually sampled

for the calculations of failure rates presented

here, because additional exclusions of respondents and intervals had to be made when data

5
necessary to the calculations were missing or

unreliable. The details of all exclusions are

found in appendix III. Many data deficiency

exclusions were necessary because of inconsistencies between information on the 3-year

month-by-month chart of contraceptive status

and the pregnancy interval data. The largest

single exclusion was of pregnancy intervals for

which the intention of contraception (to prevent

an unwanted pregnancy or deIay a wanted pregnancy) could not be determined. Because intention is strongly associated with failure rates,

results are presented separately’ for the two

categories, and intervals with unknown intention

were excluded.

The number of contraceptive use intervals

excluded because of data deficiencies was large;

the population whose experience is actually

represented in this study consists of about 10.0

million women, less than one-half the population to which the results are intended to apply.

However, since the criteria used for exclusions

are unrelated to the characteristics of the sample

of women, the exclusions ensure data accuracy

without compromising representativeness. Some

characteristics of the study population and the

population it is intended to represent are shown

in table A. Differences between the estimated

proportions in each category in the applicable

and study populations are small and reach statistical significance in only three categories:

compared to the applicable population, the

study population has proportionally more

women with less than 12 years of education,

more women from the South, and fewer women

from the Northeast. These differences were significant for white women considered separately,

but there were no significant differences for

black women considered separately. Even the

statistically significant differences were generally

Table A, Number of ever-married women 15-44 years of age who had at least one interval of entirely marital contraceptive use between

July 1, 1970 and July 1, 1973 (applicable population) and the number of women from that population whose information was

sufficient to be included in this study (study population) by rata, and percent distribution by religion, education, geographic

region, and place of rasidence: United States, 1973

Religion, education, geographic region,

end residenca

All women ...........................................

Total ....................................................

Raligion

Catholic ...............................................................

Othar and none ....................................................

Education

Lessthan 12 years................................................

12 years ...............................................................

More than 12 years ..............................................

Geographic region

Northeast .............................................................

North Central .......................................................

South ...................................................................

West .....................................................................

Residenca

Metropolitan ........................................................

Nonmetropolitan .................................................

All races White I

Black

Applicable Study Applicable Study Applicable Study

population population population population population population

Number in thousands

23,299 I 9,991 II 21,314 I 8,B14 [ 1,748 I 1,075

Percent distribution

100.0

27.1

72.9

24.2

48.7

27.0

20.0

26.1

33.0

20,9

71.0

29.0

100.0

24.8

75.2

27.3

47,4

25.3

12.3

27.3

38.1

22.3

69.2

30.8

100.0

2B.3

71.7

23.1

49.4

27.4

19.8

26,9

31,6

21.8

69.9

30.1

100.0

26,3

73.7

25.9

48.4

25,7

11.4

28.6

35.9

24.1

67.0

33.0

100.0

10.4

89.6

36.3

43.6

20.0

23.3

19,0

50.9

6,8

81.6

18.4

100.0

9.8

90.2

38.2

42.0

19.B

21.0

18.8

55.4

4.8

85.1

14.9

6
not large, and it is unlikely that they biased the

results, especially after the introduction of the

statistical controls discussed later. Within the

limits of sampling variability, also discussed

later, the results may be taken to apply to the

population of women who had at least one interval of entirely marital contraceptive use

which began between July 1, 1970 and July 1,

1973 or which began before July 1, 1970 and

continued after that date.

Identifying the Outcome of Each

Contraceptive Use Interval

After the, identification, among the sample

women, of 6,302 eligible pregnancy intervals

containing at least one valid contraceptive use

interwd (a total of 7,747 use intervals), the outcome of each contraceptive use interval had to

be determined. For the purpose of calculating

life-table failure rates, three categories of outcome were considered: close of observation,

contraceptive failure, and stopping the use of

contraceptives for other reasons.

The close of observation occurred on July 1,

1978 except when the interview took place before September 1973. In the latter case, observation ceased at the end of the 3d month prior to

the interview to exclude the possibility of pregnancies unrecognized before the interview (see

appendix IV).

Contraceptive failure, the type of termination of contraceptive use that is the focus of the

study, occurred if the date of stopping the use

of contraceptives came after the month in which

a pregnancy began or if the date of stopping was

in the same month in which the pregnancy

began and the respondent said she had not

stopped contraceptive use at the time she became pregnant. A set of circumstances that

could have been considered as contraceptive

failure occurred if the date of stopping the use

of contraceptives was in the same month in

which a pregnancy began and the respondent

reported that she had stopped the use of contraceptives before she became pregnant, but not

because she wanted to become pregnant.b In the

bTo consider this set of circumstances as contraceptive failure assumes implicitly that the stopping of contraceptive use and the conception occurred in the same

menstrual month as well as in the same calendar month.

calculation of failure rates, this set of circumstances was included with “other reasons for

stopping” and was not considered a contraceptive failure.

Aside from contraceptive failure, contraceptive use could be stopped for a number of

reasons that are extraneous to the purpose of

this study. The respondent could stop contraceptive use in order to become pregnant. For

closed pregnancy intervals this event was defined

as occurring when contraceptive use was followed by pregnancy, with or without an intervening interval of nonuse, and the dates of stopping contraceptive use and the start of

pregnancy given in the pregnancy interval data

agreed with the information in the it-year chart

of monthly contraceptive status. The latter was

necessary to ensure that the conditions of termination of contraceptive use given in the pregnancy interval data related to the contraceptive

use interval under consideration rather than a

subsequent use interval that was ineligible. If the

information did not match, termination of contraceptive use was classified as “stopped, other.”

Stopping contraceptive use in order to become

pregnant could also apply to the method most

recently used in the open interval if the respondent was trying to conceive at the time of interview.

A change of contraceptive method also

frequently occurs. A termination of contraceptive use was assigned to this classification if the

contraceptive use interval was immediately

followed by an interval of use of a different

method or by a period of no exposure to the

risk of conception and then the use of a different method. A change of method to sterilization, however, would only have been detected if

sterilization were mentioned in the 3-year chart

as a contraceptive method foIlowing the use of

another method; that is, a change to sterilization

would be clawified as “stopped, other,” if sterilization were mentioned only in response to

questions on fecundity and not those on contraceptive use.

Marital dissolution (by separation, divorce,

or husband’s death) is another reason for stopping contraceptive use. Cases in which a period

of no exposure to the risk of conception intervened between the stopping of contraceptive use

7
and the marital dissolution were included in this

category.

No exposure to the risk of conception in the

months just prior to the end of a pregnancy interval would appear to have been a logical possibility only in the case of the open interval.

However, due to the priorities of coding, the

3-year chart could show no exposure followed

immediately by pregnancy if the pregnancy

occurred in the month exposure was resumed,

whether or not there had been use of contraceptives in that month. Hence some closed pregnancy intervals contained contraceptive use

intervals that were counted as terminating in no

exposure.

Finally, there were other circumstances

grouped in the classification “stopped, other.”

Some of these were situations in which contraceptive use was stopped before conception, but

not in order to conceive. The situation referred

to previously, in which contraceptive use had

been stopped in order to conceive but the

method in use at that point could not be positively identified, was also included in this

category.

The last step in the data preparation was the

determination of the amount of exposure to the

risk of contraceptive failure per calendar month

of use (each representing an ordinal month in

the experience of any given woman) within the

3-year observation period. “More precisely, since

we are calculating probabilities (qx ‘s) of failure

and not central failure rates (mX‘s), the adjusted

number of women entering a given month of use

must be estimated. During a contraceptive use

interval, each calendar month preceded and followed by contraceptive use constituted 1 month

of exposure. For the first month of use for any

pregnancy interval starting within the 3-year

period, only half the women were considered to

have contributed a whole month of exposure on

the assumption that the initiation of use had

occurred, on the average, halfway through the

calendar month. Since the close of observation

always occurred at the end of a calendar month,

all women who were not pregnant at the close of

the study contributed a whole final month of

exposure. As indicated previously, observation

was considered to end at least 2 months before

the interview. There being one opportunity for

termination during each calendar month, women

who experienced contraceptive failures and terminations for any other reason were considered

to have contributed a full final month of exposure. The number of months during which the

respondent reported that she was not having

intercourse was subtracted from the length of

the contraceptive use interval. Exposure was

considered to begin no sooner than the second

month following a pregnancy to allow for postpartum amenorrhea.

CONTRACEPTIVE FAILURE IN THE

FIRST YEAR OF USE

Contraceptive Intention: Prevent

Versus Delay

A variable that has proved to have powerful

explanatory value is the motivation of a woman

for using contraceptives.1$ZY4Specifically, it has

been’ found useful to classify women into two

groups: those seeking to ,prevent any further

(unwanted) births, and those seeking to delay

the next wanted birth. The procedure by which

contraceptive use intervals were defined as either

prevent or delay intervals is described in detail in

appendix VI. As can be seen from table 1, the

prevent-delay classification identifies ~oups of

women for whom contraceptive failure rates are

quite different. Because the failure rate for preventers is significantly lower than that for delayers, and because the motivation for. using

contraceptives is so different for the two groups

of women, all subsequent results are presented

separately for each group.

‘The l-year failure rates for preventers (for

all methods except sterilization) and delayers

(5:1 percent and 7.3 percent, respectively) are

far below those (about 14 percent and 26 percent, respectively) reported by Ryder. 1 The

discrepancy is due to two factors. First, as previously mentioned, the measures are quite

different. Ryder employed “extended use effectiveness,” and extended-use failure rates are

higher than use failure rates. Second, because

the entire past experience of respondents was

used by Ryder in calculating failure rates, experiences in different time periods are mixed.

Since there has been a remarkable improvement

in contraceptive effectiveness over time (as

8
Ryder himself showed by comparing first-year

failure rates for different marriage cohorts), the

average failure rate is higher than the rate computed from data for only the most recent time

period.

Age, Education, and Parity

The age of the respondent’ might be expected to have an influence on the likelihood of

contraceptive failure. First, fecundity is known

to decline with age and, other things being

equal, lower fecundity impli& that a smaller

proportion of women will experience a failure.

Moreover, advancing age probably strengthens a

woman’s motivation to terminate childbearing

but does not necessarily affect a woman’s motivation to delay childbearing. Thus age might be

expected to have a greater effect on failure rates

for preventers than delayers. As seen in table 2

and figure 1, among women attempting to prevent an unwanted pregnancy, older women had

consistently lower failure rates. On the other

hand, there is no systematic relationship between age and the failure to delay pregnancy.

The educational attainment of a woman has

been found nearly universally to be associated

with the likelihood of contraceptive failure.

Table 2 and figure 2 show that high educational

attainment was associated with low contraceptive failure rates, although the differences among

educational attainment groups is not statistically

significant. Education may indicate contraceptive sophistication, or it may represent the

opportunity cost of an unintended pregnancy.

Women with a large number of children were

expected to have high failure rates because high

parity may be due, in part, to previous contraceptive failure. In fact, it is shown in the first

column of table 2 and in figure 3 that among

preventers high parity is associated, although not

significantly, with low failure rates, except at

the very highest parity. There was no association

cSince the unit of analysis in this study is the contraceptive use interval, the age of the respondent is given by

age at her last live birtb, which is the beginning of the

birth interval from which the use interval was drawn.

For women with no live births, age at last live birth is

equal to age at marriage, the beginning of the first birth

interval.

9

8

7

6

25

:

:4

3

2

1

0

15-19 20.24 2529 30.34 35.39

AGE IN YEARS AT LAST LIVE BIRTH

NOTE Bucd.. c.nlnccptke. = !ntcrmk during which the woman wasco.tlnuously marncd

Figure 1. Percent of married women 15-44 years of age attempting to prevant an unwanted pregnancy who experienced a contraceptive failure during the first year of use

(for usersof all contraceptive methods except sterilization),

,by age at last live birth: United States, 1970-73

Pmwmot unwanted Delay wanted

pregnancy pregnancy

Qr B.e

Less 12 More Less 12 More

thm :han than

12

than

12 12 12

YEARS OF EOUCATION

NOTE: bed on c!mtrxeplmt .x mtcrvds duruv wh,ch the woman wnsConlmuo. sly reamed

Figure 2. Percent of married wornen 15-44 years of age who experienced a contraceptive failure during the first yeer of usa

(for usersof all contraceptive methods except sterilization),

by contraceptive intantion and education: United States,

1970-73

9
8

r

7.4

ioro

NUMBER OF CHILOFIEN

NOTE Bawdon oonmceptlveuw Intend, durln~ which tha wonm wm cmtlnucmly mnni,d.

Figure 3, Peroent of marriad women 15.44 years of age at.

tampting to pravent an unwanted pragnancy who axperl.

ancad a contraceptlva failure during tha first yaar of usa

(for usersof all contracaptiva methods axcapt steriilzation),

by parity: United Statas, 1970.73

between parity and contraceptive failure rates

for women attempting to delay pregnancy.

Subsequent analyses involving race, religion,

geographic region, marriage cohort, and method

should be cross-tabulated by these three control

variables—age, education, and parity-in addition

to intention.

Relative Age

Ryder found that age, education, and parity

had no systematic association with contraceptive

failure rates when the effects of these variables

were examined within categories of “relative

age.” He noted that a woman who had her third

pregnancy at age 23 was in some sense younger

(younger at a comparable stage in the family life

cycle) than a woman who had her first pregnancy at 23. He therefore defined a variable

called “relative age” which was determined

jointly by the order of pregnancy interval and

the age of the woman at the start of the interval.

Ryder used a ~h=ee-~tep procedure for

coding relative age. First, the sample women

were ordered according to age at first marriage

(the start of the first pregnancy interval) and

divided into four age groups (low, low middle,

high middle, and high). The upper age limits of

the three youngest age groups were then used to

define the upper age limits of these groups for

higher order pregnancy intervals: 2 years were

added to the limits for the second pregnancy

interval, 4 years were added to the limits for the

third pregnancy interval, and so on. Finally, a

woman was assigned an appropriate relative age

group for each of her pregnancy intervals according to her age at the beginning of the interval and the defined age limits. However, as a

consequence of this arbitrary addition of 2 years

to define age limits and of the truncating of

some of the birth cohorts, the relative age categories were unevenly represented within each

pregnancy order; the magnitude of the observed

differentials between relative age categories is

partly a function of this uneven representation,

If the lowest relative age represented the same

fraction of women for each order, the proportions failing for relatively young women would

have risen with birth order from order Itwo to

order five,

In response to this problem it was decided,

for this report, to define the relative age categories in terms of the age quartiles of the unz’-

verse of women arriving at the beginning of

intervals of each order, and to include all intervals in this universe, regardless of whether contraceptives had been used in the interval. It was

also decided that birth intervals rather than

pregnancy intervals should be used. There were

two reasons for this decision, The primary

reason is practical. Pregnancy interval data may

be unreliable because of the propensity of

women to underreport pregnancies ending in

spontaneous abortion. The secon’d reason is that

relative age may influence fertility decisions primarily through the joint effect of the number of

children (births, not pregnancies) and the

woman’s age.

To mitigate the truncation effect of a crosssections.1 sample, it was necessary to use lifetable techniques to determine the proportion of

women arriving at the beginning of birth intervals of each order at each age. Because the

sample is truncated, however, the numbers

actually falling into each category tend again to

be uneven and weighted toward the young ages.

Since the universe is defined to comprise all intervals, however, there is a compensating bias

among the intervals eligible for the analysis of

10
contraceptive failure, because noncontracepting

women, whose intervals are by definition excluded from the analysis of contraceptive failure, are likely to arrive at the beginning of each

interval at a younger age than contraceptors.

Because of the difficulty of specifying the

date of the beginning of exposure to the risk of

conception, Ryder considered only intervals

following a pregnancy, that is, intervals of order

2 and higher. In this report intervals of use were

included in the analysis if use of the method

began after marriage (see appendix 111for exceptions). Thus the relative ages of women in the

first birth interval were coded with reference to

the date of marriage and the quartile age limits

used were those of the second birth interval

(that between the first and second births),

minus 1 year.

The upper age limit of each of the first three

quartiles for birth orders 1-6 are shown in table

B. The first, second, ad third quartile age limits

are the ages at which the cumulative probabilities of having a birth of a given order are 25 percent, 50 percent, and 75 percent, respectively,

of the overalI probability of ever having a birth

of that order (by exact age 45). The calculations

were also made by 5-year birth cohorts of

women, but among women who were old

enough to have had sufficient exposure to the

possibility of births of any given order no significant time trends were discernible.

In summary, we have modified the definition of relative age proposed by Ryder. The

present definition provides a classification by

the age of a woman at the beginning of a birth

interval which would be comparable for intervals

of every order. As can be seen from table IV in

appendix VII, there is no systematic variation by

parity, education, or age within the relative age

groups. The inference is drawn that any independent effect of these variables is subsumed in

the relative age classification. This consideration

reaffirms and strengthens the analytical importance of the relative age concept.

Method of Contraception

Failure rates vary widely according to the

contraceptive method used (table 3 and figure 4). The most successful contraceptive

method observed in this study was sterilization,

with no reported failures. Sterilization was followed by the oral contraceptive pill and the IUD

which were both more effective than any of the

remaining, coitus-related, methods of contraception (although among preventers the difference

in failure rates between the diaphragm and

either the pill or IUD did not attain statistical

30

25

20

1-

E

g 16

it

10

5

0

Pill Iuo @tiOm Disphragm F.mm, crmm, Rhythm

and jelly

CONTRACEPTIVE METHOO

NOTk B,~d O“OM!,WP,,VCwe ,ntev,l’dur,n~wh,<hthewomanw,, .w1,.u,wI, ,,u,,wJ

Figure 4. Percent of married wornen 15-44 years of age who experiancad a contraceptive failure during the first year of

use, by contraceptive intention and contraceptive mathod:

United States, 1970-73

Tabla B. Quartile upper age limit for ever-married woman 1544 years of age, by birth order and quartila: Unitad States, 1973

Birth order

Quartile

o 1 2 3 4 5

6 or

or higher

I

Age in years

First quartile ......................................................................................... 17.21 18,21 20.73 22.92 24.60 26.20 28.18

Second quartile ..................................................................................... 19.39 20.39 23.31 25.66 27.87 29.72 30.52

Third quartila ........................................................................................ 22.41 23.41 26.46 29.11 31.27 33.40 33.83

11
significance).d The pill was used with equal success by both preventers and delayers; 2 percent

of pill users in each intention category experienced a contraceptive failure during the first

year of use. IUD users attempting to delay a

wanted pregnancy were somewhat less successful

users than those attempting to prevent an unwanted pregnancy but the difference is not significant. Among condom users, preventers were

much more successful than delayers were in

their use of the method, and exhibited less than

half as many first-year failures. Preventers using

the rhythm method were also more successful

than delayers. Their 1-year failure rate was less

than one-third that of rhythm method delayers.

Although differences in failure rates among

women in different relative age categories were

not significant for any contraceptive method,

the rates for the condom consistently decreased

as relative age increased, The same pattern, with

a few inconsistencies was found for the other

coitus-related methods (foam, diaphragm,

rhythm) and for the pill among delayers. Among

preventers, the failure rates for the pill were not

related to relative age. The IUD is the major exception to the general pattern and is discussed in

a later section,

Because there is a great demand for a single

failure rate to be assigned to each contraceptive

method so that methods can be easily compared,

a standardized failure rate for each method is

presented in table C. Since some cells in table 3

contain data derived from a very small number

of women, it was not possible to standardize by

both relative age and intention. Hence the data

are standardized by intention only. The procedure for standardizing is a ,matter of choice; one

may weight the failure rates by the distribution

of months of exposure to the risk of conception

or by the distribution of the number of intervals

entering the 12-month life table. Fortunately,

either procedure yields the same result; the proportions of either intervals or months are almost

evenly split between prevent and delay. Hence

the standardized rate is the simple arithmetic

average of the two.

‘The standard error of the diaphragm failure rate for

preventers is extremely large (5.6 percent) due to the

small number of women who reported using that

method.

Table C. Percent, standardized by contracaptiva intention, of

married women 1 15-44 years of age who experienced a

contracaptiva failure during the first year of usa, by

contraceptive method: United States, 1970-73

Contraceptive mathod I

Contraceptive

failure

Pill ...................................... ............................

lUD .................... .................. ...........................

Condom .............................................. ............

Foam, cream, and jelly ....... .............. ...... .........

Other ..............................................................

Diaphragm .......................................... .......

Rhythm .....................................................

Otherz .......................................................

I

Percent

2.0

4.2

10.1

14.9

14.5

13.1

19.1

‘10.8

lThe results are based on contraceptiveuse intervals during

which the woman was continuously merried, but the woman

need not have been married during the entire 3-year period covered by the study.

2J?,~cIllde~sterilization.

The standardized failure rate is the percent

of women who would fail in the first year of

contraceptive use among a group of women with

equal proportions of delayers and preventers. In

actual populations of users, the proportions who

are preventers and delayers vary among contraceptive methods, so the “raw,” or unstandardized failure rates, would differ from the standardized rates shown. These rates are higher for

methods in which delayers predominate, and

lower for methods in which preventers predominate. In practical situations in which the intention of contraceptive use is known, the

intention-specific rate for preventers or delayers

should be used; if nothing is known about intention, the standardized rate is appropriate.

Race

A common finding of recent studies of

contraceptive utilization is that black women are

less likely than white women to use contraceptives, but black contraceptors are more likely

than white contraceptors to use effective

methods. A report published by the National

Center for Health Statistics which analyzed the

current body of data was consistent with this

assertion.E As can be seen from table 4 and figure 5, black women were more successful than

white women were in delaying a wanted pregnancy. This pattern is consistent within all rela12
Preventunwanted Dday Wit~Od

pregnancy prwnmcy

‘r 7.4

White 818ck , White Black

RACE

NOTE:Bawdm emtmeptlw umIntervalsduringwhkhthew.anmwascontinuouslymarried,

Figure 5. Percent of married women 15-44years of age who experienced a contraceptive failure during the f irst yaw of use

(for usarsof all contraceptive mathods-except sterilization),

by contrecaptive intention and race: Unitad States, 1970-

73

tive age groups, although the differences are not

significant. Among women who were attempting

to prevent an unwanted pregnancy, there was no

consistent pattern by relative age group, but for

all age groups combined, white women in the

sample used in this study had a 12 percent lower

failure rate in the first year than black women

had. These data (table 4) also support Ryder’s

observation that black women, unlike white

women, are apparently no more successful when

their intention is to prevent an unwanted pregnancy than when delaying a wanted pregnancy.

This pattern varies by relative age gToup, but

when all relative age groups are combined the

failure rate for black preventers is higher (but

not significantly) than that for black delayers.

White women, on the other hand, were clearly

more successful when their intention was to

prevent rather than to delay a pregnancy.

Since the intervals of contraceptive use

which entered the life tables are a subsample of

all contraceptive intervals, it is interesting to

look at the distribution of contraceptive

methods used by race among this subset of intervals. Since sterilization, the pilI, and the IUD

have been shown to be the most effective contraceptive methods, they are grouped together

for this analysis. The failure rate by race is a

function of both the distribution of contraceptive use intervals by method, and of months of

exposure per contraceptive use interval which

are included in the life table. Thus, for each

method (~r group of methods) there is a choice

of presenting the distribution either of intervals

or of months of exposure to the risks of conception which occurred during contraceptive use

intervals included in the analysis. Neither alone

determines the rate, so the choice is a matter of

preference. For this analysis, months of exposure was chosen. Fortunately, the two distributions are remarkably similar so that either choice

gives the same result.

As can be seen from table D, within the

Table D. Percent of months of exposure to the risk of conception 1 during the first year of contraceptive use for women who*

intention was to prevent an unwantad pregnancy, during which the pill, IUD, or sterilization were used, and during which the IUD

was used, by relative age and race: United States, 1970-73

Relative age

Contraceptive method and race

Total Low Low High High middle middla

Pill, IUD, or sterilization Percent

White ................................................................................................................................... 68.6 79.3

Black

71.9 70,4 62.7

................................................................................................................................... 76.2 83.7 “ 83.3 77.2 67.9

—IUD

Whita ......................................,..........!....,., .......................................................................... 9.7 8.1 10.6

black.,...,.,, .............................................................................................eom....m.......oo.e.o...o..m.

12.0 7.4

14,0 7,5 10.4 21.1 13.4

lincludes only those months which occurred during contraceptive use intervals included in the analysis.

13
sample of women used in this study, black preventers were more likely than white preventers

were to use the most effective contraceptive

methods at all relative ages. In particular, in the

higher relative age groups, they were more likely

than white women were to use the IUD.

Hmce, the higher failure rates for black

women who sought to prevent an unwanted

pregnancy might be due to their less effective

use of the more effective contraceptive methods,

especially the IUD. This inference is supported

by table 5, which presents a breakdown of failure rates by method and race. (An insufficient

number of cases in many cells precludes further

breakdowns by relative age.) Among women

who were attempting to delay a wanted pregnancy, black women were somewhat, but not

significantly, more successful users of every

method except the pill. Among black and white

preventers, pill effectiveness was roughly equal;

but the IUD failure rate for black women in the

sample was considerably higher than that of

sample white women, a finding that was unexpected. While sample size was too small for an

adequate test af this relationship, the large difference exhibited by women in the sample

points to the need for a further examination of

IUD use on the basis of additional data. In conclusion, there does not appear to be an unambiguous racial difference in effectiveness of

usage.

Religion

Previous research found that the probability

of a contraceptive failure varies by religion.1 In

this report, failure rates were compared for two

categories of religion, Catholic and “other or no

religion. ” These categories were chosen because

they were expected to exhibit the greatest difference in failure rates between any two religious groups, and because data limitations preclude any further breakdown.

In recent years, Catholic women have increasing y abandoned the rhythm method for

more effective methods of contraception. The

change from rhythm is especially pronounced

after the last wanted child has been born. With

this change in contraceptive use by Catholic

women has come a remarkable improvement in

their contraceptive efficacy; few of the previously observed differences by religion remain

(see table 6 and figure 6).

Among white women, the difference in

failure rates of Catholic women and women of

other religions is not significant either for those

trying to prevent an unwanted pregnancy or for

those trying to delay a wanted one. Further,

among preventers, Catholic women were slightIy

more successful contraceptive users at every

relative age but one. If sterilization is excluded

from the analysis, the religious differential

among preventers increases, demonstrating that

white Catholic women are less likely to use

sterilization and are even more successful users

of the remaining methods.

Prevent unwantnd

pregnancy

9

8

7

8 [

DelOy wantti

pregnancy

none none

RELIGION

NOTE. Basedon contraceptive useintorvds during which the woman wascontinuously married,

Figure 6. Percent of married white women 15-44 years of age

who experienced a contraceptive failure during the first

year of use (for users of all contraceptive methods except

sterilization), by contraceptive intention and religion:

United States, 1970-73

Marriage Cohort

Ryderl found that the more recent the marriage cohort, the more effective was contraceptive use when examined within contraceptive

intention and relative age categories. He interpreted these findings as resulting from an upward trend in efficacy over time because the

experience of the most recent cohorts was

14
limited to the most recent time periods in which

contraceptive efficacy was high; much of the

experience of the older cohorts occurred during

periods of low efficacy. A possible alternative

explanation, however, is that the differences in

the faiIure rates of different cohorts are due to

cohort effects: The most recent cohorts have

Iower failure rates because their members were

more likely to use more effective contraceptive

methods or to use the methods more effectively,

independent of the time period observed. Since

the current data are Iimited to one time period

(1970-73), it should be possible to determine

which of these two explanations is more likely.

Given that the effects of differences in age

among the members of different cohorts are subsumed under relative age groups, if cohort differences are due to time period effects, then within

one time period there should be no cohort differences in failure rates. Conversely, if the rate

differences are due to cohort effects, then within one time period the older cohorts should have

higher failure rates.

Table 7 shows that if there is any systematic

association “of marriage cohort with failure rates

among preventers, it is not that suggested by the

hypothesis that efficacy has been increasing for

the most recent cohorts. Although the differences are not significant, earlier cohorts were

generally more successful preventers. No systematic differences among delayers”are seen. An

important point to note, however, before concluding that only period rather than cohort

changes in efficacy have occurred, is that any

differentials by marriage cohort measured in a

specified time period reflect both true cohort

differences and any confounding life cycle differences not captured by the relative age categorization. Since these two effects work in

opposite directions (by hypothesis, the older the

cohort, the higher the failure rate; the longer the

marital duration, the lower the failure rate),

results such as those found in table 7 might be

obtained even if a cohort trend toward higher

efficacy exists. However, such a trend seems

likely to be small. Therefore, although we cannot separate with certainty a time period from a

cohort marital-duration effect, tabIe 7 strongly

suggests that improvement in efficacy over time

was the major contributor to the large cohort

cumulated life-time differentials observed by

Ryder.c

Place of Residence

Contraceptive failure is related to the geographic re~on in which a woman lives. As seen

in table 8, the proportion of sample women who

failed to prevent an unwanted pregnancy was

more than twice as great for women who lived in

the North Central and West Regions as for those

who lived in the South. The influence of geographic location on failure rates is probably not

independent of the age, education, and parity of

women: but a paucity of cases prevents further

breakdown. There does not appear to be any

association between failure rates and residence

in metropolitan or nonmetropolitan areas (see

table 9).

FAILURE RATES AT HIGHER

DURATIONS

Because of the cross-sectional nature of the

3-year chart of monthly contraceptive status,

the first-year failure rates selectively represent

the experience of women who began a continuous segment of contraceptive use (although not

necessarily for the first time) no earlier than

11 months prior to July 1, 1970. The vast majorityf started using contraceptives during the

3-year interval covered by this study. In order to

have started using a method during that period,

such women must have (1) changed methods,

(2) terminated a pregnancy, or (3) (remarried.

On balance, their termination rates reflect the

experience of less successful users. Thk point is

perhaps made clearer by the fact that women

who had been successful contraceptors for at

‘A corollary would be that Ryder’s pronounced upward trend in effectivenessof use is underestimated,

since all segments of contraceptive use, including the

most recent and therefore most successful, were employed when calculating the failure rates for each,

especially the oldest, cohort.

‘2,148 of 2,503 delay-use intervals and 2,293 of

2,691 prevent-use interwds, respectively, started during

the %ycar interval.

15
least a year before July 1, 1970 and who successfully avoided pregnancy during the 3-year

period without changing methods would not

appear in the 12-month life table at all. Because

the life tables are multiple increment, their experience would, however, be counted at higher

durations of use. It is interesting to explore the

experience of such long duration users.

First- and second-year failure rates are given

in table 10. Second-year failure rates are somewhat lower than first-year rates (see figure 7).g

There are two possible explanations for lower

rates in the second year. First, the probability of

failure may vary over women; hence, only (on

the average) more successful users are represented in the second-year failure rate. Second,

failure rates may decline over time for individual

women. We cannot distinguish empirically between these two causes; regardless of cause, on

the average the second-year failure rates reflect

the experience of more successful contraceptive

users. Table 11 shows the first- and second-year

failure rates for the pill, the only method for

gsi~ficmce cannot be determined since standard

errors ;f second-year failure rates are not available.

Preventunwanted

8

[

pregnancy

7

6

t 5.1

Delay wanted

pregnancy

7.3

1St 2nd 1St 2nd

YEAR OF uSE

NOTE Bwsd.. mntraceptiwwe intmvnl$duringwhich the woman was continuously mxnkd.

Figure 7. Percent of marriad women 1544vears of age who experienced a contraceptive failura during”the first ;nd second

yaars of use (for users of all contraceptive methods except

steriIization ), by contraceptive intention: United States,

1970-73

which there is a sufficient number of months of

exposure to warrant separation.

The same logic applies to’ failure rates at

even higher durations of use, but further examination of these data are precluded by the relatively small number of months of exposure over

the durations from 3 to 5 years.

EXTENDED USE EFFECTIVENESS

A consistent finding in the analysis of contraceptive use failure rates is the remarkable

overall uniformity and, small proportion of

women who experienced a contraceptive failure.

Within relative age and intention categories there

is little variation in failure rates by religion, race,

marriage cohort, or education. This study does

show some variation, but not the large range

noted by Ryderl. There seems t-o have been a

convergence in efficacy among subdivisions of

the population among which one might have

strong a priori reasons for suspecting, differentials. However, the convergence may simply be

due to a different method of measuring failure

rates. To test this possibility, Ryder’s definition

of extended use effectiveness was employed to

compute the proportions of women who failed

to prevent or delay pregnancy in the first year of

a segment of contraceptive use. Recall that if

contraceptives were used in any pregnancy interval, an unintended pregnancy was, counted as a

failure even if no contraceptives were being used

when the pregnancy occurred. Ryder included

all intervals in the pregnancy history in his

study; here only those which began or ended between July 1, 1970 and July 1, 1973 were considered. Except for the definition of exposure to

the risk of a failure, the methodology used to

compute extended use-failure rates is identical

to that for use-failure rates described previously

and in appendix IV. Thus differences in usefailure rates compared to extended use-failure

rates are due to differences in the measurement

of exposure to the risk of conception. Table 12

shows extended use-failure rates for wornen in

the sample used in this study. When measured in

this way:

1. The differentials by religion are small

and are confined, as in table 6, to those

16
whose intention was to delay their next

wanted pregnancy.

2. For delayers, black women had much

higher failure rates than white women

had, in contrast to the rates shown in

table 4; for preventers the differentials

were larger than in table 4.

3. The association between contraceptive

failure and the educational attainment of

women is maintained, with those of

higher educational attainments having

lower failure rates, but the spread is

larger than that shown in table 2.

It may be concluded that extended use

effectiveness is a measure of a type of contraceptive failure in which both method nonuse and

failure during use are contributing factors. Differentials in extended use effectiveness are due

primarily to intergroup differences in the nonuse of contraceptives. However, convergence is

indeed occurring even when efficacy is measured

in this way.

CONTINUATION RATES

Although the use-fai~ure rates presented in

the preceding sections are low, at least in comparison to extended use-failure rates previously

available, the discontinuation rates are not. Because measures of discontinuation of contraceptive use for reasons directly associated with a

method of contraception were desired, continuation rates were calculated in three ways, each

eliminating some reasons for stopping use. Table

13 shows continuation rates in which the only

reasons for stopping are “stopped, other” and

“change of method,” where unintentional pregnancy is not included. Table 14 gives continuation rates in which all method-related terminations (including unintentional pregnancy) are

included. The first set of rates measures the extent to which women discontinue use of a contraceptive method because of dissatisfaction

with that method; the second set of rates adds

contraceptive failure to the reasons for discontinuation.

o A final measure of continuation of contraceptive use that is of great interest is the proportion of women who would continue to use

contraceptives if the only cause of discontinuation were %topped, other.” Women who stop

using contraceptives altogether are exposed to a

substantially higher risk of unintended pregnancy than those who change methods. Thus the

continuation rates measured in this way, presented in table 15, indicate the attractiveness of

a contraceptive method in the vitzd sense that

discontinuation implies abandonment of contraceptives altogether. This measure is identified

cIosely with Ryder’s concept of extended use

effectiveness; the relationship is explored in

detail in the final section of this report.

Three reasons for stopping contraceptive use

were excluded in calculating the rates in tables

13-15–stopped to get pregnant, stopped because

marriage was dissolved,h and stopped because

exposure to the risk of conception was ended.

One additional reason–unintended pregnancy–

was eliminated in table 13, and an additional

category, change of method, was eliminated in

table 15. The methodology underlying each

calculation is identical to that underlying the

calculation of failure rates given in appendix IV.

For this reason the product of the proportion of

women continuing to use contraceptives, derived

from table 13, and the proportion of women not

experiencing a contraceptive failure (1.0 minus

the proportion experiencing a failure, derived

from table 3) equals the proportion of women

continuing contraceptive use shown in table 14.

Similarly, the product of the proportion of

women not experiencing a contraceptive failure

and the appropriate proportion continuing contraceptive use, derived from table 15, yields the

proportion continuing contraceptive use if the

only causes of contraceptive failure are pregnancy and “stopped, other. ” The proofs of these

assertions are given in appendix IV. As expected,

women in the sample were Iess likeIy to continue using any contraceptive if their intention

was to delay the next wanted pregnancy rather

than to prevent an unwanted one. If the condition “stopped to get pregnant” were added as a

cause of discontinuation of contraceptive use,

‘This category does not imply that women stopped

using contraception after their marriage was dissolved

but simply indicates that they were excluded from the

analysis.

17
the proportions of women continuing to use

contraceptives among those who wished to delay

pregnancy would be much lower, A comparison

of the 12-month continuation rates in table 14

with the 12-month failure rates in table 3 shows

that when all reasons for stopping contraceptive

use are combined, the risk of an unintended

pregnancy is small relative to the total methodrelated risk.

THE RELATIONSHIP BETWEEN

EXTENDED USE EFFECTIVENESS,

USE EFFECTIVENESS, AND

CONTINUATION RATES

Earlier in this report, the differences between extended use effectiveness and use effectiveness were discussed. It was argued that

extended use failure rates could be misleading

since it is not possible to distinguish failures that

occur during the use of a contraceptive method

from those which occur after a method is

abandoned. Later, use and extended use-failure

rates were presented, and several measures of

continuation of contraceptive use were shown.

It is useful to examine the relationships between

these measures,

It is convenient to frame the discussion in

terms of l-year rates, but the argument applies

to rates for any duration of time. Since the rates

involved are life-table rates, they represent the

experience that cohorts of women, would have

had if they were subject to the monthly failure

rates produced by the life table. Women who did

not experience a contraceptive failure in the extended use sense can be divided into two categories: (1) those who did not fail to prevent

pregnancy and used contraceptives for an entire

year, and (2) those who discontinued contraceptive use during the year, did not change to

another method, and yet did not become pregnant. In probability terms

Pe =“Pc+ P~ (1)

where

Pe is the probability of not becoming

pregnant as measured by extended use

effectiveness,

PC is the probability of not becoming

pregnant and continuing to use contraceptives, and

pd is the probability of discontinuing

contraceptive use and not bl~coming

pregnant.

The term Pc can be viewed as the product of

two terms: the probability Pu, of not failing (not

becoming pregnant) as measured by use effectiveness rates, and the probability C of continuing contraceptive use if the only cause of discontinuation is “stopped, other” (abandonment of

all contraception), The probabilities Pe and C are

derived from the rates ,shown in tables 12 and

15, respectively; the rates from which the Pu

probabilities are derived are scattered throughout many other tables in this report. From

equation 1 we see that extended use-failure rates

cannot be recreated from knowledge of use

effectiveness rates and continuation rates alone.

One must also know the term Pd, which is a

function not only of the overall proportion of

women (1 - C) who stop using contraceptives,

but also of the particular pattern of discontinuation over the 12-month period. For example,

given a value of C, if all women who discontinue

contraceptive use did so at the end of the first

month of use, the proportion of discontinues

who became pregnant would be much higher

than if all women who discontinue did so at the

end of the 1lth month of use. The term pd is

also a function of the fecundability of women

who discontinue contraceptive use. However, as

a first approximation we treat fecundability as

biologically constant for all women at every

duration of exposure to the risk of conception.

Then pd is merely a function of the pattern of

discontinuation and a natural constant (fecundability).i

Thus, pd can be separated into two factors:

Pn, the probability of a woman not becoming

pregnant given that contraceptives use is abandoned and (1 -C), the probability that the use of

lIn principle the probabilities of a woman becoming

pregnant for each month after the cessation of contraceptive use can be computed by the same life-table procedures employed to measure use effectiveness. However, the small numbers of women involved make the

calculated monthly pregnancy rates extremely unstable.

18
contraceptives is discontinued. Note that Pn is

still a function of the pattern of discontinuation.

The purpose of this factorization is to identify

a discontinuation level factor C and a discontinuation pattern factor Pn. The factor Pn can

be identified only approximately with the pattern of discontinuation since it is not true that

fecundability is the same for all women and

every duration. Nevertheless, even this approximate measure is instructive.

It was mentioned earlier that while contraceptive use effectiveness rates showed little

variation by race, the extended use effectiveness

rates suggest that black women in the sample

were less effective contraceptors. We can now

examine the components of this discrepancy. In

table E, the terms Pe, Pc, Pd, Pu, Pn, &d k are

presented as an illustration of the decomposition

of extended use effectiveness. It can be inferred

that kunple black women did not have lower

extended use effectiveness rates than white

women had solely because they had lower continuation rates. Among sample women whose

intention was to prevent an unwanted pregnancy, if black women had had the same continuation rate as white women, their extended

use effectiveness rate would have been 94.5 percent, rather than 92.1 percent, but would still

have been below the rate for white women (95.2

percent). When this measure is used, approximately three-quarters of the racial difference is

due to the larger proportion of sample black

women who abandoned contraceptive use altogether.j The remainder of the difference can be

attributed to the relatively earlier discontinuation among black women than among white

women who discontinued. This conclusion is

supported by the detailed life-table continuation

rates computed as those for table 15 but not

shown; for example, 73 percent of those discontinuing contraceptive use among sample black

women but only 51 percent of those discontinuing among white women had done so by the

end of the sixth month.

jof course, there is an index number problem. If

white women were assigned the continuation rate of

black women, their extended use effectiveness rate

would fall to 0.932; hence, only two-thirds of the difference is explained by differences in continuation rates.

Tabla E. Estimates of components of extended use effactivaness ratasl for married women2 15-44 years of age, by contraceptive

intantion and race: Unitad States, 1970.73

Contraceptive intention and race

Prevant unwanted pregnancy3

Whita ...................................................................................................

Black ...................................................................................................

Delay wanted pregnancy

Black ...................................................................................................

Components of extended use affectivenass rates

Pe I

PC IP“

0.952 0.934 0.953

0.921 0.876 0.958

0.877 0.836 0.926

0.859 0.843 0.862T

c f’d

0.970 0.018

0.914 0.045

0.903 0.041

0.876 0.016

P“

0.600

0.523

0.423

0.129

(1 -c)

0.030

0.066

0.097

0.124

lPe=PC+pd.

PC= PU. C.

pd=p~(l-~.

Pe= Proportion of women not becoming pregnant in 1 year measured by extended use effectiveness (1 - extended use failure rate/

100).

PC= Proportion of women not becoming pregnant end using contraceptives for 1 “year.

Pd = Proportion of women who abandoned contraceptive use and did not become pregnant within 1 year.

Pn,= The conditional probability of not becoming pregnant given that contraceptives were abandoned in the particular pattern observed over the course of the firstyear since use begsn,

C = One-Yearcontinuationrate, when the only cause of failure is “stopped, other.”

Pu= Proportion of women not becoming pregnant in 1 year as measured by use effectiveness (1 - use faiture rate/100).

2The results are based on contraceptive use intervals during which the woman was continuously married, but the woman need not

have been married during the entire 3-year period covered by the study.

31ncludes sterilization.

19
REFERENCES

lRyder, Norman: Contraceptive failure in the United

States. Fare. Plann. Perspect. 5(3): 130-142, Summer,

1973.

2Ryder, Norman, and Westoff, Charles: Reproduction in the United States, Princeton, N.J. Princeton University Press, 1971, Chap. XI, pp. 295 ff.

~Tietze, Christopher, and Lewit, Sarah: Statistical

evaluation of contraceptive methods: Use-effectiveness

and extended use-effectiveness. Demography 5(2): 931-

940, May 1968.

4Sagi, philip C., Potter, Robert G. Jr., and WeStOff,

Charles F.: Contraceptive effectiveness as a function of

desired family size. Population Studies 16(1 ): 291-296,

March, 1962.

5Nation~ Center for He~th statistics: Advance Data

Contraceptive utilization in the United States: 1973 and

1976, No. 36. DHEW Pub, No. (PHS) 78-1250. Aug. 18,

1976, Public Health Service, Hyattsville, Md.

6National Center for Health Statistics: The National

Survey of Family Growth, Cycle I; sample description,

estimation procedures and variance estimation, Vital and

Health Statistics. Series 2-No. 76, DHEW Pub. No, (PHS)

78-1350.

7Nation~ Center for He~th Statistics: Statistics

needed for national policies related to fertility; A report

of the United States National Committee on Vital and

Health Statistics. Vital and Health Statistics. Series 4-

No. 18. DHEW Pub. No. (PHS) 78-1455,

8Bureau of the Budget: Standard Metropolitan Statistical Areas, Washington, U.S. Government Printing

Office, 1967.

9Potter, Robert: Application of life table techniques

to measurement of contraceptive effectiveness. Demography 3(3): 297-304, Aug. 1966.

lo~letze, Christopher, and Lewit, Sarah: Evaluation of

intrauterine devices: Ninth progress report of the Cooperative Statistical Program. Stud. Fare. Plann. 2(7):

July1970.

11Balakrishnan, T. R., Allingham, J. D., and Kantner,

J. F.: Analysis of oral contraceptive use through multiple decrement life table techniques, Demogra~h*j 7(4):

459-65, NOV. 1970.

12Lewit, SZWA: TWO years experience with the

Copper-T: A research report. Stud. Fare. Plann. 4(7):

171-2, July 1973.

13pierce, A., Hiller, J. M,, and McGuire, J.: A tom.

pasison of two large-scale studies of the use-effectiveness

of IUD’S. Stud. Fare. Plann. 3(9): 205-13, Sept. 1972.

~4Sivin, Irving: The effectiveness of the Copper-T intrauterine device: A collaborative study in five countries.

Stud, Fare. Plann, 4(7): 162-170, July 1973.

15V~muktanon, Sasichm, and Rosenfield, ~lm: An

IUD follow-up study in Potharam, Thailand. Stud. Fare.

Plann. 2(8): 166-170, Aug. 1971.

16Sinquefield, Jeanne Cairns: Single and lK.dtiple

Decrement Life Table Procedures for the Analysis of the

Use Effectt”veness of Contraception. Family Planning Research and Evaluation Manual #8. Community and Family Study Center, University of Chicago, 1973.

17Tietzei Christopher: Intra-uterine contraception:

Recommended procedures for data analysis. Stud. Fare.

Plann. Vol. 1 (supplement), Apr. 1967.

18~letze, Christopher, and Lewit, Sarah: Recommended procedures for the statistical evaluation of intrauterine contraception. Stud, Fare. Plann. 4(2): 35-42, -

Feb. 1973,

19Chiang, Chin Long: Introduction to Stochastic

Processes in Biostatistics. New York. John Wiley, 1968.

20Potter, Robert, Chow, L. P., Jain, A. K., and Lee,

C, H.: Effectiveness of intrauterine contraception: Termination levels and correlates, and R. Potter, Useeffectiveness of intra-uterine contraception as a problem

in computing risks, in Ronald Freedman and John

Takeshita, Family Planning in Taiwan. Princeton. Princeton University Press, 1969.

21Preston, Samuel, Key fitz, Nathan, and Schoen,

Robert: Causes of Death: Life Tables for National Populations. New York, Seminar Press, 1972.

22Schoen, Robert, and Nelson, Verne: ~~~riage,

divorce and mortality: A life table analysis. Demography

11(2): 267-290. May 1974.

20
LIST OF DETAILED TABLES

1, Percent of married women 15-44 years of age who experienced a contraceptive failure during the firat year of use, and the

standard error of the percent, by contraceptive method end intention: Unitad States, 1970.73 ................................................

2, Percent of married women 1544 years of age who experienced a contraceptive failure during the first year of usa, and the

standard error of the percent, by contraceptive method and intention, age at last live birth, education, and parity:

United States, 1970-73 ....................................................................................................................................... ......................

3. Percent of married women 1544 years of aga who experiancad a contraceptive failure during the first year of use, and the

standard error of the percent, by relative aga, contraceptive intention and contraceptive method: United States, 1970-73 ......

4. Percent of married women 15-44 years of age who exparianced a contraceptive failure during the first year of usa, and the

standard error of the parcent, by relative age, contraceptive intention, contraceptive mathod, and race: U nitad States,

1970-73 ................................................................................................................................ ................................ .....................

5. Parcant of married women 15-44 years of age who experienced e contraceptive failure during the first year of usa, and tha

standard error of the percent, by contraceptive mathod, contraceptive intention, and race: United States, 1970-73 ................

6. Percent of married white women 1544 years of age who experienced a contraceptive failure during the first year of use, and

the standard error of tha percent, by ralative age, contraceptive intention, contraceptive mathod, and raligion: United States,

1970.73 ....................................................................................................................................... .................... ..................... .....

7, Parcent of married women 15-44 years of age who experienced a contraceptive failure during the first year of use, and the

standard arror of the percent, by ralative age, contraceptive intantion, contraceptive method, and year of marriage:

United States, 1970-73 .............................................................................................................................................. ................

8. Percent of married women 1544 years of age who experienced a contraceptive failure during the first year of use, and the

standard error of the percent, by contraceptive intention and method and geographic region: United States, 1970-73 .............

9. Percent of married woman 15-44 years of age who experienced a contraceptive failure during tha first year of usa, and the

standard error of the parcent, by relative age, contraceptive intention, contraceptive mathod, and place of residence:

United States 1970-73 ..........................................,,,,,,. ,,,.............................................................................................. .............

10. Percent and standard error of the percent of married women 1544 years of age who experienced a contraceptive failure

during the first year of use, and the percent who experienced a failura during the second year of use, by relative age, contraceptive intention, and contraceptive method: United States, 1970.73 ..................................................................................

11, Percent and standard error of the percent of married women 15-44 years of age using the oral contraceptive pill who axparienced a contraceptive failure during the first year of use, and the percent who experienced a failure during the second year

of use, by relative age and contraceptive intantion: United Statas, 1970.73 ..............................................................................

12. Percent of married women 15.44 years of aga who bacame unintentionally pregnant within 1 year after baginning use of a

contraceptive method, regardless of whether use was atopped at any time during that period, by raletive age, contraceptive

intention, race, religion, education, and contraceptive method: United States, 1970.73 ...........................................................

13, Percent of married women 1544 years of age who continuad to use tha same contraceptive mathod, if only method-related

reasons for stopping (excluding unintended pregnancy) ara allowed, by contraceptive intention, months since use begen,

contraceptive method, race, education, and religion: United Statas, 1970.73 ...........................................................................

14. Parcent of married women 15-44 years of age who continuad to usa the same contraceptive method, if only method-related

reasons for stopping are allowed, by contraceptive intention, months sinca use began, contraceptive method, race, aducation,

and religion: United States, 1970.73 ................................................................................................................................ .........

15. Percent of married women 15-44 years of aga who continued to usa tha same contraceptive method, if abandonment of

contraceptives altogather is the only reason for stopping that is allowed, by contraceptive intention, months since use began,

contraceptive method, race, education, and religion: Unitad States, 1970.73 ...........................................................................

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

21
Table 1. Percent of married womenl 15-44 years of age who experienced a contraceptive failure during tha first year of use, and the

standard error of the percent, by contraceptive method and intention: United States, 1970-73

All

Contraceptive intention

All methods

methods except

steri Iization

I

Percant

Prevent unwanted pregnancy ........ ..... .............................. .. ........ ...................................................................... 3.7 5.1

Delay wanted pregnancy ................................................................. ........ ........ .............. .............. .. ..............S..O . . . 7.3

I

Standard error

Prevent unwanted pragnancy .. ........................................ ....................... ............................ ................ .. ........ .... 0.45 0.61

Delay wanted pregnancy .......... ...... .. ...... .. ................ ............ ............................ .......... .. ...... .. ...... ....... C............. . . . 0.76

lThe *esult5 are based on contraceptive uae intervals during which the woman was continuously married, but the woman need IIOt

have been married during the entire 3-year period covered by the study.

NOTE: In this report percents that have a standard error that is 25 percent or more of the estimate itself are considered “unreliable.”

The reader is advised to use caution in interpreting results involving unreliable estimates.

,

.

22
Table 2. Percent of married womenl 15-44 yeers of age who experienced e contraceptive failure during the first year of use, end the

standerd error of the percent, by contraceptive method and intention, age et last live birth,2 education, and parity: United States,

1970-73

Aga at last live birth, education, and parity

Age at last live birth

20-24 years .....................................................................i .......................... ..............................................

25-29 years ..............................................................................................................................................

30-34 years ..............................................................................................................................................

35-39 years ..............................................................................................................................................

Education

Less than 12 yaars ...................................................................................................................................

12 years ...................................................................................................................................................

More than 12 years ..................................................................................................................................

Parity

No live Mrths ...........................................................................................................................................

One live birth ..........................................................................................................................................

Two live births ........................................................................................................................................

Three live births ......................................................................................................................................

Four live births ........................................................................................................................................

Five live births .........................................................................................................................................

Six live births or more .............................................................................................................................

Age at last Iiva birth

15-19 years .............l..l .........................................................c........l..........................................................

20-24 years ..............................................................................................................................................

25.29 years .................................................................................. ...................................................... ......

30.34 years..4 .....................................a...............a...................................................a.a...............a...............

35-39 years ......................................................................................................................................... .....

Education

Less than 12 years .................,,, ,,, ............................................................................................................

12 years ........................................................................................................................................ ..0.,,...,.

More than 12 years ..................................................................................................................................

Parity

No live births ............................................................................................... ................................ ...,....,.4,

Ona live birth .................... ............................................................................ ..........................................

Two live births ........................................................... .............................................................................

Three live births .....................,, ,0,,..............!4............................................................. ....................,.. .,.,,,,

Four live births .,., ..............................................................!! ....................................................................

Fiva live births ,,,...,, ,. ...............................................................................................................................

Six live births or mora ....................................................................................................... ,4,0,.............,,,.

1

Prevent unwanted Delay

pregnancy

wanted

pregnancy

All

methods

;::

2.9

1.6

1.1

4.2

3.8

2.9

5.0

4.4

4.6

3.1

2.1

1.6

4,4

2,31

1,06

0.62

0.68

1.15

0.64

0.79

0.90

3.38

2,03

0.81

0,85

0.81

:::

Percent

8.4

7.9

4.2

2.4

1.5

6.3

5,2

4.0

5.9

5.1

::

3.2

2.5

7.4

Standard error

2.92

1.30

0.90

1,01

1.60

1.26

1.10

1.24

3,97

2,36

1.05

1.30

1.20

2.27

3.51

9.9

5.6

8.4

7.3

●

8.6

7.2

6.5

7.5

5.s

9.6

4.1

19.8

●

●

1.84

0.93

1.85

5.10

. . .

2.43

0,97

1,33

1.28

1,32

2,26

2.17

9.87

. . .

. . .

lThe results me based on contraceptive use intervals during which the woman was continuously married, but the woman need nOt have been

married during the entire 3-year period covered by the study.

2Since the “nit of analys~ in th~ study IS the contraceptive use interval, the age of the respondent is given by her age at leSt live birth, which is

the beginning of the birth interval from which the use interval was drawn. For women with no Uve births, age at lest live birth is equal to age at

marriage, the beginning of the first birth interval.

NOTE: In this report percents that have a stsmdsrd error that is 25 percent or more of the estimate itself are considered “unreliable.” The

reader is sdvised to use caution in interpreting results involving unreliable estimates.
Table 3. Percent of married womenl 15-44 years of age who experienced a contraceptive failure during the first year of usa, and the

standard error of the parcent, by relative age, contraceptive intention and contrawptive method: United States, 1970-73

Contraceptive intention and contraceptive method

Prevent unwanted pregnancy

All methods2 ............................ .........................................................................

Pill .................. ................................ .................. .................................................................

IUD ......... ........................................ .......... ............ ...................4...... ................. ...J.............

Condom .......... .................. ................................................................................................

Foam, cream, and jelly ...... ................................................................................................

0ther3 ...............................................................................................................................

Diaphragm ....................................................................................................................

Rhythm ................. ................................................................ .......................................

0ther3 ................................................... ................................ .......... ...... ........ ...............

Delay wanted pregnancy

All methods ...... .. ........ .............. .........................................................................

Pill ........ .... ................................................................................... .................................. ,..,

IUD ............................................................ .................................................................... ...

Condom ...................... ...... ........ .. ...... .. .......... ...... .. ........ ........ ........ .. .............. .. ...... ........ ....

Foam, cream, and jelly ........ ................................................. ......... ........ ........ .................. ..

Other ..................................................... .............. .................. .................. ..........................

Diaphragm ............................ .. .......................................................... ................ ............

Rhythm ............................ ......................... ........................................ ........ .. ................ .

Other ................. ....... .............. .................................. ................ ........ ............................

Al I methods2 ......... .............................. ................. ................................. ............

Pill ............................................... .. ...... .................. .............. ..............................................

iUD ................. ...... ................ ...................... .................................... ..................................

Condom ................ ......................................... .............. .................................... ..... ... .........

Foam, cream, and jeily ................. ........ ........ ........ .......... .......................... ...... .. .................

0ther3 ............................................................................................ ................ ...................

Diaphragm .................. ...... ....................... ............................ .........................................

Rhythm ........................... ........................ ................... ...... ......... .................................. .

0ther3 .............. .......... ...................... ...... ........ .................. .......... ..................................

Delay wanted pregnancy

All methods ..... ........ .................... .......... ........ .. ................ .. ...................... .. ........

Pill ................. .......... .................................................................!..... ........ ... ........................

lUD .......................... .............................................. .................. ...... ........ ...........................

Condom ............ .............................................................. ................ ..................................

Foam, cream, and jelly ................................... ........ ........................................ .......... ...... ...

Othar ........ ...... ............... .. ........ ........................ ...... ........ ................ ............ ............ ............

Diaphragm ......... .............................................. ................. .... ............... .........................

Rhythm ..................................... .............. ................... ...... ......................... ........... ..... ...

Other ............................................................................................................................

Relative age

Percent

3.7

2.0

2,9

6.6

13.1

8.5

10.3

9.5

6.5

7.3

2,0

5.6

13.7

16.7

20.4

15,9

28.8

15.1

0.45

0.67

1.42

1.92

3.68

. . .

5.58

4.09

. . .

0.76

0.50

2.21

2.73

3.42

3.28

5.30

5.39

5.54

8.5

2.8

23.4

46.2

*

*

*

*

11.0

5.7

6,9

48,3

*

*

*

*

*

4,5

1,8

2.3

9.8

15.6

13.2

*

*

5.6

8.1

2.2

3.2

22.0

34.5

21.1

*

*,

20.7

Standard error

1.64

2.27

. . .

21,08

. . .

. . .

. . .

. . .

3.40

3.59

7.42

20.40

. . .

. . .

. . .

. . .

. . .

1.01

1,24

2.30

6.10

5.17

. . .

. . .

. . .

. . .

1.71

1.00

2.89

8.33

9.56

7.64

. . .

. . .

. . .

2,9

2.’1

7.’1

8.0

8.2

11.1

14:?

0.9

6.2

I CJ

4.6

10.7

7.6

25.9

27.~

39.2!

6.5

0.88

—.

1.43

2.20

3.32

4.99

. . .

12.86

8.71

. . .

0.99

0.57

3.36

4.56

3.75

5.39

. . .

. . .

. . .

2.1

1.2

5,0

2.2

5.4

4.8

4.2

5.4

4.3

6.7

0.8

7.6

9.1

11.1

16.0

4.3

23.6

19.1

0.51

0.88

3.43

1.55

4.28

. . .

4.33

3.78

. . .

1.35

0.64

3.73

4.45

6.01

5.30

. . .

. . .

12.25

lThe ~esult~ are based on ~~ntrac~pti~e use internals dufig which the woman was continuously married, but the woman need nCrt

have been married during the entire 3-year period covered by the study.

21n~l~de~ stefili~atio~.

3Excludes sterilization.

NOTE: In this report percents that have a standard error that is 25 percent or more of the estimate itself are considered “unreliable.”

The reader is advised to use caution in interpreting results involving unreliable eatimatea.

24
Table 4. Percent of married womenl 15-44 yaars of age who experienced a contraceptive failure during the first year of usa, and the

standard error of the percent, by relative age, contraceptive intantion, contraceptive mathod, and race: United States, 1970-73

Contraceptive intention, contraceptive method, and race

PREVENT UNWANTED PREGNANCY

All methods

White ................................................................................................................................

Black ................................................................................................................................

All methods except sterilization

White ................................................................................................................................

DELAY WANTED PREGNANCY

Al I methods axcept sterilization

White .................................................................................................................................

Black .................................................................................................................................

PREVENT UNWANTED PREGNANCY

All methods

White .................................................................................................................................

Black .................................................................................................................................

Al I methods except steril ization

White ................................................................................................................................ ,

Bleck .................................................................................................................................

DELAY WANTED PREGNANCY

All methods except staril ization

White .................................................................................................................................

Black .................................................................................................................................

Relativa age

Total IILow I

Low High I

High

middle middla

II I I

3.7

4.2

5.1

6.0

7.4

3.8

0.49

1.44

0.67

2.02

0.76

1.72

9.6

2.8

15.6

4.3

12,6

1.2

Percent

4.5

4.7

6.2

6.1

8.3

5.0

1.95

1.30

3.30

1.93

3.87

0.92

Standard error

1.07

1.61

1.40

1.96

1.81

4.63

3.6

1.7

4.8

2.1

6.2

4.4

0.93

0.85

1.21

1.08

0.95

3.29

1.8

6.9

2.6

10.5

6.8

3.7

0.50

3.96

0.71

5.58

1.36

1.86

lThe ~esul~ are b~ed on contraceptive u~~temale dufigwhichthe woman was continuously married, but the womsn need not

have been married during the entiie 3-year period covered by the study.

NOTE: Inthisreport percents tiathave aatindmd emorfiat ia25percent ormoreof theestimate i*elfme considered ``unreEable.''

The reader is advised to u= caution in interpreting results involving unreliable estimates.

25
Table5. Percent of married womenl 15-44 years of age who experienced a contraceptive failure during the first year of use, and the

standard error of thepercent, bycontraceptive method, contraceptive intention, and race: United States, 1970-73

Contraceptive intention and race

Prevent unwanted pregnancy

Whita ........... ................ .. .................... ........ .. ...... ........ .............. ........ .. ...... .. .. .......... ...........

Black ............................. ...................................... ...... ................ .......................................

Delay wanted pregnancy

White ................................ ........ ....................................... .. ...................... ...... ...................

Black ................................................... ................................. ......................... ..................

Prevant unwanted pregnancy

White ...... .................................................. ............... ...................... ...................................

Black ..................................................... .. ...................................... ...................................

Delay wanted pregnancy

White .. ............................ ....................... ............... ....................... .....................................

Black ................... .. .............. .................. ..... ................................................. .....................

IEEE

. . .

. . .

. . .

. . .

2.1

1.9

2.0

2.6

Percent

2,4

8.1

5.1

3.2

Standard error

5.65

0.92

0.52

1.98

1.43

7.43

2.30

2.12

6.7

4.4

14.1

8.2

2.00

2.92

2.78

7.46

10.2

12.2

19.4

7.8

2.18

4.90

2.31

6.71

lThe ~e~ults are based on con~aceptive ~Se intervals during which the woman was continuously married, but the woman need not

have been married during the entire 3-year period covered by the study.

NOTE: Inthisreport percents that have astandard error thatis25percent ormoreof theestimate itself reconsidered ``u~nreliable.''

The reader ia advised to use caution in interpreting results involving unreliable estimates.

26
Table6. Percent of married whita womanl 15-44years of Wewhoexperienced acontra&ptive failure during the first yearofum, and

thestandard error of thewrcent, byrelative Wa, contraceptive intention, contramptive mathod, and religion: United States, 1970-73

Contraceptive intention, contraceptive method, and religion

PREVENT UNWANTED PREGNANCY

All methods

Catholic .............................................................................................................................

Other and none .................................................................................................................

All methods excem steril ization

Catholic .............................................................................................................................

Other and none .................................................................................................................

DELAY WANTED PREGNANCY

All methods except sterilization

Catholic .............................................................................................................................

Other and none .................................................................................................................

PREVENT UNWANTED PREGNANCY

All methods

Other and none .................................................................................................................

All mathods except sterilization

Catholic .............................................................................................................................

Other and none .................................................................................................................

DELAY WANTED PREGNANCY

All methods except sterilization

Catholic .............................................................................................................................

Other and none .................................................................................................................

Relative age

Total IILow I

Low High High

middle middle

3.3

3.8

4.3

5.5

8.7

6.7

4.7

11.2

7.1

18.1

13.9

11.6

Percent

4.3

4.6

5.7

6.4

10.9

7.3

1

0.88 4.82

0.62 2.55

1.14 7.08

0.80 4.42

1.39 12.17

0.86 3.51

Standard error

2.23

1.58

3.01

2.15

3,14

2.02

3.9

3.5

4.8

4.8

6.1

6.2

1.42

1.12

1.73

1.54

2.07

1.29

1.7

1.9

2.3

2.7

9.3

5.1

0.97

0.62

1.34

0.89

2.28

1.56

lThe ~e5ult~are based on contraceptive use intervals during which the woman was continuously married, but the womim need not

have been married during the entire 3-year period covered by the study.

NOTE: In thisreport percents that have askndmd error that is2Spercent ormoreof theestimate itseIfare considered ``unreliable. ''

The reader is advised to use caution in interpreting results involving unreliable estimates.

27
Table7. Percent of married womenl 15-44 years of age whoexperienced acontracaptive failure during the first year of use, and the

standard error of the percent, by relative age, contraceptive intention, contraceptive method, and year of marriaga: United States,

1970-73

Contraceptive intention, contraceptive method, and year of marriage

PREVENT UNWANTED PREGNANCY

All methods

1970.73 ........................ ... .............................. ...... .......................................... ....................

1965-69 ................. ........................ ...... .. ........ ........ ...... ................................ ......................

1960-64 ................. .............. .. .............. .................. ...... ................ ....0.... ..................... ........

1955.59 ........#.............................................................. ........ ...............#...............aB.....n.....#.

All methods except stabilization

1970.73 ................ ............ .......... ........ ...... .. ...... .. ........ ...... .. ...... ................ ........ .. ...............

l%5.69 ............................. ........ .............................. .........o........................ ................ .... ....

1960.64 ..................... ................................ .............. ...a.............. ...................... ..................

1955.59 ............................................. ........ ............................a... ........................................

DELAY WANTED PREGNANCY

All methods except stabilization

1970-73 ....................,..,.,.,,,., .................... ...... .................. ........ ...... ........ .. ...... .. ............ .. ...

1965-69 .......................... ....................... ............... ........ .................................. ........ ...........

1960S4 .......................................................... ...... .. ...................... .. ............................. ......

PREVENT UNWANTED PREGNANCY

All methods

1970.73 ................ ........ .. .............. .............. ........ ........ .. .............. .......... ........ .. ...... ...... .......

196569 ...................................................... .. .............................................. .. ........ .............

1960-64 ....... ................................ ........................................ ...... ........ .. ...... ........................

1955.59 .............. ................ .. .......8s........................... .......................... .......... ................ .....

All methods except sterilizetion

1970.73 ............................l .........o....... ............. ................................... ...... .................. .......

196549 ............ .......... ....................................... ..... ...........................................................

1960-64 .................,. .,, ,.,,.,,.., ,., ..,, ,,, .,,.,. ................................,,, ................................ .. ...... ..

1955.59 .......................o.........m. .........................#o...... ........ .................................................

DELAY WANTED PREGNANCY

Ail methods except sterilization

1970.73 ...............<................ ........n....................... .................................. ...... .. ...... ...... ......

1965%9 ....... .......................... ...... ................ ........................................ ..............................

1960-64 .. ..............,., ,.,, .,,,..... ........ .............. ........ .......................................... .................0...

Relative age

Total Low Low High High

middla middle

5,4

7.0

3,4

1.9

6.8

8.8

4.7

3,0

6.9

7,2

8.8

2.98

1,42

0.71

0.69

3.75

1.77

0,99

1.07

1.04

1.03

2.90

4.1

12.8

11.2

6.5

20.0

15.7

1.5

19.8

*

Percant

0.5

10.1

2,2

0.7

12.8

3.1

8.2

6.9

11.3

15.00

3.61

4.71

17.61

6.26

6.64

1.46

6.53

. . .

. . .

2.78

1.22

. . .

3.57

1.71

. . .

2,22

6.81

5.;’

6.1

3.4

1,8

6A

7.2

4.:1

2.9

7.5

4,5

7.5

. . .

2,25

1.47

1.28

. . .

2.54

2.08

1.99

1,38

1.43

4.66

10.6

2.0

2.4

3.1

12.6

2.5

3.3

4.7

6.3

7.1

7.7

12.04

1.35

1.14

1.27

14.71

1.74

1.52

1.86

2.50

1.64

3.52

lThe ~esult5 are based ogcontra~eptive~~e inte~a~ during tilch the woman was continuously married, but the womanneednot

have been married during the entire 3-year period covered by the study.

NOTE: In this report percents that have astandard emorthat is25percent ormoreof theestimate itself areconsidered ``unreliable. ''

The reader is advised to use caution in interpreting results involving unreliable estimates.

28
Table8. Percent of married womenl 15-44 years of agewhoaxperiencad acon&aceptNe faiiure during the first year of use, andthe

~andard error of thepercent, bycontramptive intention andmethod and geographic region: Unitad States, 1970-73

Geographic region

Northeast ................................................................................................................................

North Central ................................................................................................................m..,.,..

South ......................................................................................................................................

West .......................................................m...................m.....m......................................................

Northeast ................................................................................................................................

North Central ..........................................................................................................................

South ......................................................................................................................................

West ........................................................................................................................................

Pravant unwanted Delay

pregnency

wented

pregnancy

Percent

2.7

4.5

2.2

5.7

0.69

0.75

0.45

1.88

3.5

6.6

2.9

9.4

Standard error

0.83

1.05

0.57

3.46 I

9.1

:::

6.9

2.15

1.50

1.07

1.89

lThe results are based on contraceptive use intervals during which the woman was continuously married, but the women need not

have been married during the entire 3.year period covered by the study.

NOTE: In this report percents that have a standard error thatis25 percent or more of the estimate itself are considered “unreliable.”

The reader is advised to use caution in interpreting results involving unreliable estimates.
Table 9. Percent of married women 1 I 5.44 years of agewho experienced a contraceptive failure during the first year of use, and the

standard error of the percent, by relative age, contraceptive intention, contraceptive method, and place of residence: United States,

1970-73

Contraceptive intention, contraceptive method, and residence

PREVENT UNWANTED PREGNANCY

All methods

Metropolitan ....... ............. ......................................o... ...............<....44. ...@@.40tj ... ....o.oo.<...4..4.

Nonmetropolitan .. ........ ........................ .............. ...........8............ ...m.. ........ ...m..o.......c@...m..44

All methods except sterilization

Metropolitan ................... ........ ....................................o.4........................omm........<mt.......t4....

Nonmatropoiitan ..................................................... ....c<................ ......c..@...c.t..t......o..........

DELAY WANTED PREGNANCY

All methods axcept sterilization

Metropolitan ........ .............. ........ .. ................ ...... ........ ...... .......... .........om...t4.0.....@o.c..ott .......

Nonmetropolitan .........................................<..............<<.............<...........m.c..o.oom.....c....coo@....

PREVENT UNWANTED PREGNANCY

All methods

Metropolitan ............. V...... .. ...... ................. .............<. .............. ........ .......<44...o.08m..........o.co.m

Nonmetropolitan ........ ...... ................ .. ...................................... ................ ........ .................

All methods excapt sterilization

Metropolitan ................ .. ........ .............................................. ...... .. ...... .. .............................

Nonmetropolitan ... ................................ ........ .............................................<.......t ..............

DELAY WANTED PREGNANCY

All methods except sterilization

Metropolitan ........................... .................................................. .............o........ ........c....+@.{.

Nonmetropolitan ...... .................. .............. .......... .... .............................. .. ................ .. ....c....

Relative age

*

3.7

3.7

5.3

4.8

7.8

6.0

0.!52

0.82

0.74

1,06

0.94

1.24

8.8

8.1

14.4

12.7

11.8

9.2

Low High

middle middle

Percent

4.8

4.0

6.7

5.2

8.2

8.0

2.05

2.77

3.24

4.87

4.62

4.79

Standard error

0.98

2.57

1.37

3.17

2.26

2.78

3.6

3.2

4.9

4.1

6.7

5.1

1.04

1.50

1.38

1.97

1.15

2.01

High

2.0

2.5

2.9

3.3

7.8

3.8

0.54

1.28

0.78

1.60

1.70

1.88

lThe results are based on contraceptive use intervals during which the woman was continuously married, but the woman ]neednot

have been married during the entire 3-year period covered by the study.

NOTE: In this repotipercents that have astandard error thatis25percent or more of theestimate itself areconsidered’’unreliable.>>

The reader is advised to use caution in interpreting results involving unreliable estimates.

30
Table 10. Percent and standard error of the percent of married women 1 15.44 years CSfage who experienced a contraceptive failure

during the first year of use, andthepercent who'experienced afailure during thewcond year of usa, byrelative age, contracepnve

intention, and contraceptive method: United States, 1970-73

Contraceptive intention and contraceptive method

FIRST YEAR

Prevent unwanted pregnancy

All methods . ........ ........ ........ ............ ........ ............ ........ ...... .............. .......... ...... ..................

All methods except sterilization ............... .......................................... ............................ ...

Delay wanted pregnancy

All methods except sterilization ........................................................................................

SECOND YEAR

Prevant unwanted pregnancy

All methods ......................................... ........ ..................................................................... .

All methods axcept sterilization ................. .............. ................ ............ .......... ............ .......

Delay wanted pregnancy

All methods except sterilization ... ........ .. ........ ...... ...... .. ............................ .. ...... .............. ...

FIRST YEAR

Prevent unwan~ed pregnancy ‘

.,

Relative age

Total Low Low High High middle middle

3.7

5.1

7.3

2.4

3.3

5.2

8.5

13.7

11.0

3.7

“ 6.3

6.9

4.5

6.2

8.1

2.2

3.1

6.1

Standard error

“3.5

4.7

6.2

1.6

2.2

3,8

All methods

L

......................................................... ........ ................................................ ...... .

All methods except sterilization .. ................................ ............................................ ......”.. .

Delay wanted pregnancy

All methods except sterilization ....... ...................... .. ...... .............. ..................................... .

lThe results are bawd on co~t~~c~ptive uw intervals during which the woman was continuously married; but the woman need SIOt

have been married during the entire 3-year period covered by the study.

NOTE: In this report percents that have a standard error that is 2S percent or more of the estimate itself are considered “unreliable.”

The reader ia advfsed to use caution in interpreting results involving unreliable estimates.

2.1

3.0 “

6.7

2.7

3.7

6.2

0.51

0.71

1.35

.,

31

. . .
Table 11. Percent and standard error of the percent of married women I , S.u ~ear~ of age using the oral contraceptive Pill who

experienced a contraceptive failure during tha first year of use, and the percent who experienced a failure during the second year of

use, by relative age and contraceptive intention: United States, 1970-73

Contraceptive intention

First year

Prevent unwanted pregnan~ ........ ........... ........................................ ...................... .......... ..

Dalay wanted pregnancy ....... ........................................ .......................... ................ ..........

Second yaar

Prevent unwanted pregnancy .................................. .. .........................................................

Dalay wanted pregnancy .......................................... ................ ........ .................................

First year

Pravent unwanted pregnancy ......................................... .. ........................ .. ...... ...... ........ ....

Delay wanted pregnancy ............ .................... ................ ................ .. ...... .......... ........ ...... .. .

Ralative age

Percent

2.0

2.0

1.1

1.8

2.8

5.7

0.7

5.0

s.-

1.8

2.2

0.3

0.1

Indard error

2.9

1.5

2.2

2.4

1.2

0.8

0.8

1.1

0.67 I2.27 1.24 1.43 0.88

0.50 3.59 1.00 0.57 0.64

lThe results are based on contraceptive use intervals during which the woman was continuously married,” but the woman need not

have been married during the entire 3-year period covared by the study.

NOTE: In this report percents that have a standard error that is 25 percent or more of the estimata itself are considered “unreliable.”

The reader is advised to use caution in interpreting results involving unreliable. eatbnates.

32
Table 12. Percent of married womenl 1544 years of age who becama unintentionally pregnant within 1 year after beginning use of a

contraceptive mathod, regardless of whether usa was stoppad at any time during that period, by relativa age, contraceptive intention, race, raligion,2 education, and contraceptive mathod: Unitad Statas, 1970-73

,.

Contraceptive intantion, race, raligion, education, and contraceptive method

PREVENT UNWANTED PREGNANCY3

All preventers ....................................................................................................................

~

Whiw .................................................................................................................................................

Black ........................................................................................................................................ .........

I!Q!Q!Z

Catholk .............................................................................................................................................

Other and none .................................................................................................................................

Education

Less than 12 yaars .............................................................................................................................

12 years .............................................................................................................................................

More than 12 years ...................................................................................................." ......................

Contramptiva method

Pill ........................................................................................................................................... ..........

IUD .......................................................................................................................................... .........

Foam, craam, and jelly ......................................................................................................................

All othar methods .............................................................................................................................

DELAY WANTED PREGNANCY

All delayers .....................................................................................................!.... .............

Race .

Black ................m................................................................................................................................

I!!?!k@

Cetholic ......................................................................................................................................... ....

Other and none .................................................................................................................................

DELAY WANTED PREGNANCY

Education

Less than 12 yeers .............................................................................................................................

12 years .............................................................................................................................................

Mora than 12 years ............................................................................................................................

Contraceptive method

IUD ...........................................................................................”. .. ....... . .......................................

Condom ........................................................................................................................................... .

Foam, cream, and jelly ......................................................................................................................

All other mathods except Werilization ...............................................................................................

Ralativa age

Total Low Low High High

middle middle

Percent

5.0

4.8

7,9

4.8

4.9

6.0

%

3.8

5.6

1:;

9.5

12.4

12.3

14.1

14.7

11.1

16.7

12.1

10.5

7.0

10.0

20.0

225

24.5

9.4

~

10.4

4.9

4.7

11.9

13.9

0.9

●

3,2

24.8

50.0

●

20.1

20.5

19.2

26.4

18.4

23.0

14.2

●

17.5

●

49.2

●

●

7.0

6.9

9.1

8.6

6.2

6.2

7.4

8.0

5.7

5.5

13.0

18.3

15.2

12.0

~

12.1

10.0

“ 15.0

11.0

14.6

11.8

7.7

4.8

E

40.6

27.2

5.0

4.8

8.5

4.4

5.0

3.7

5.5

4.9

4.5

5.3

7.3

15.4

8.4

12.2

12.0

14.1

13.5

11.2

6.8

12.3

12.8

7.6

11.7

18.4

13.3

28.4

2.6

2.2

8.4

2.3

2.1

1.8

3.2

2.3

1.7

7.4

2.2

5.3

5.9

10.5

10.5

14.3

14.1

8.1

18.0

11.7

8.9

3.0

11.8

13.8

16.1

21.0

lThe ~e~ults are bssed on contraceptive MC ~terv~$ dufig ~lch the woman was continuously msrried, but the woman need not have ben

married during the entire 3-year period covered by the study.

2Results for religion are based on the contraceptive use intervets Of white Women OSllY.

31nclu&s sterilization.

33
Table 13. Percent of married womenl 15-44 years of age who continued to use the same contraceptive mathod, if only mathod-related

raasons2 for stopping (excluding unintended pragnancy) are allowed, by contracaptiva intention, months since use began,

contraceptive method, rata, aducation, and religion3: United Statas, 1970-73

Contraceptive mathod, race, education, and raligion

All woman4 ........................................................................................................

Contracaptiva mathod

Pill .......................................m..............................................................................................

IUD ................................................................................................................................ ....

Condom ..............................................................................................................................

Foam, craam, and jelly .......................................................................................................

All other mathods axcapt sterilization ................................................................................

Race4

Education4

Less than 12 yaars ..............................................................................................................

12 yaars.....................................0........................................................................................

Mora than 12 yaars .............................................................................................................

Religion4

Catholic ..............................................................................................................................

Other and nona...................................................................................................................

Delay wanted Pravent unwantad

pregnancy pregnancy

Months since use began

xI+01121’’’o’o

Percant

70.9

75.8

76.2

66.5

56.5

64.0

70.4

74.5

71,1

72,6

68.4

68.6

71,3

57.6

59.4

67.4

55.6

48.1

54.6

57.3

64.7

57.4

58.2

56.8

56,1

58.3

34.1

30.6

51.8

42.7

28.8

40.9

33.8

35.9

43.1

35.8

26.6

31.5

34.9

77.2

72.7

77.9

64.2

57.9

70.8

77.4

73.3

78.0

77.6

75.7

78.9

76.7

68.5

59.1

70,,2

57<,1

49.3

=,,7

68,,8

62,6

70,2

69(,5

65,0

69,4

68,5

51.2

33.0

54.6

46.3

27.6

46.7

51.0

50.1

E4.3

52,4

45.4

51.9

50.6

lTheres”lts are based on contraceptive lISe intervals dur~g which thewomanws continuously married, but the woman need not

have been married during the entire 3-year period covered by the study.

2Method-related reasons for stopping contraceptive use are unintended pregnancy, stopped to change methods, and “stopped,

other, ''which istheabandonment ofcontraceptives altogether. Unintended pregnancy isnotincluded as a reason.

3Results for religion are based on the contraceptive use intervalg of white womon only.

41n~udes sterilization for preventers.
TabIe 14. Parcentof married womenl 15-~years ofagewho continued touwtha mmacontraceptive metiod, ifonlymethod.related

reasons2 for stopping are allowed, by contraceptive intention, months since uw&@n, contraceptive method, race, education, and

religion3: United Statas,1970-73

Contraceptive method, rata, education, and religion

All women4 ........................................................................................................

Contraceptive mathod

Pill ......................................................................................................................................

Condom ..............................................................................................................................

Foam, cream, and jelly .......................................................................................................

Another methods axceptstarilization ................................................................................

Race4

White ...................................................................................................................................

Black ..................................................................................................................................

Education4

Lessthan 12 years ..............................................................................................................

12 years ...............................................................................................................................

More than 12 years .............................................................................................................

Raligion4

Catholic ..............................................................................................................................

Other and nona...................................................................................................................

Delay wanted Prevent unwanted

pregnancy pragnancy

Months since use began

12 24 60 72 24 60

Percent

65.8

74.3

71.9

57.4

47.1

51.0

65.2

71.6

65.0

67.3

63.9

62.6

m.5

50.6

57.1

60.2

44.5

32.5

38.4

50.2

58.2

48.5

50.9

51.1

46.6

52.0

28.6

~

28.2

45.3

28.8

15.1

13.7

26.6

26.7

36.0

27.1

21.0

23.1

28.3

74.4

71.2

75.6

60.0

50.3

64.7

74.5

70.2

74.7

74.7

73.5

76.3

73.8

54.4

57.2

67.5

51.4

39.6

49.6

64.6

59.0

65.0

65.8

61.3

65.6

64.2

44.8

31.5

48.7

37.1

16.7

31.9

44.5

45.6

46.5

47.2

38.5

44.6

44.5

lTh&re~lts are baaed on contraceptiveuae intervals during which the woman wascontinuoualy married, but thewoman need not

have been married during the entire 3-year period covered by the study.

2Method.related reaaons for atopp]ng contraceptive “se me ~n~tended pre~ancy, stopped to change methods, and “atopped,

other,” which is the abandonment of contraceptive altogether.

3@@ts for religion are breed on the contraceptive use intervals Of White WOmen onlY.

41ncludes aterili~ation for preventers.

35
Table 15. Percent of married womenl 15-44 years of age who continued to use the same contraceptive method, if aband(cnment of

contraceptives altonather2 is the only reason for stooping that is allowed, by contraceptive intention, months sinca use began,

contraceptive method, race, education; andraligion3: United States, 1970-73

Contraceptive method, race, aducation, and religion

All women4 ........................................................................................................

Contraceptive method

Pill ....................................m.................................................................................................

IUD ............... ....... ........ .. .......................... ...... ............ .......... ............ ........ ........ ..................

Condom ............................... .. ..... .......................... ................ ............ ........ .. ...... ..................

Foem, cream, and jelly ......... ...................... .... ...... .................................... ............ ...... ........

All othar methods except sterilization ....................... ........... ....................4.. .......................

Race4

White ......................... .......... ........ .......................................................................................

Black ................... ................ ...... .................. ........................ ............ ...................................

Education4

Lassthan 12 years .............. .............. ........ ................ ........ ................................ ...... ............

12 years ..... ..m............... .............. .................o.... ........................ ...................... .. ...................

More than 12 years .......................... ........................................................ .............. .. ........ ...

Religion4

Gtholic .................... ........ ........ ........................o.............. ..........o..................o.. ...................

Other and none ...................................................................................................................

I

~“fted

Months since use bagan

12 24 60 12 2’4 60

90.3

89.7

93.7

91.5

91.0

8B.6

90.3

87.6

86.0

90.9

91.3

89.6

90.6

81.3

80.2

89.0

64.4

78.5

79.4

81.3

80.7

75,9

80.9

84.7

78,5

82,7

Percent

61.3

57.3

78.7

73.0

58.0

59.5

61.7

52.9

58.6

63.1

57.3

53.9

65.5

96.6

~

94.5

95.1

96.6

92.5

97.9

97.0

91.4

94.4

97.5

97.0

97.0

96.9

94.9

90.5

94.0

95.3

90.3

97.6

95.7

85.3

92!.1

96.1

95.5

95.3

95.9

——

91.0

82.9

92,4

92.7

80.7

94.3

92.2

76.1

86.2

91.7

95.0

91.7

90.6

lThe ~e~ults ~ro based on contraceptive “ae intervals d~r~g which thE woman was continuously married, but the woman need not

have been married during the entire 3-year period covered by the study.

Zwomen whom reason for stopping contraceptive use was classified S5

.

“stopped, other” were considered to have abandoned

contraceptives altogether.

3Results for religion are based on the contraceptive use intervals of white women fJnlY.

‘$Includes sterilization fOr preventers.

36
APPENDIXES

CONTENTS

I. Technical Notes .............................................................................................................................

Background ...............................................................................................................................

Statistical Desi~ .......................................................................................................................

Measurement Prmess .................................................................................................................

Data Reduction .........................................................................................................................

Reliability of Estkates .............................................................................................................

Nonsarnpling Emor ....................................................................................................................

Interview Nomesponse ..............................................................................................................

Item Nonresponse .....................................................................................................................

IL Definition of Terns ........................................................................................................................

IIL Selection of Smple ......o.......o..................................o....................................o..........................o......

IV. The Calculation of Gross Rates of Continuation for Contraceptive Methods: Sk@ and Multiple

Increment Life Tables ....................................................................................................................

Preliminary Manipulation of the Data ......................................................................................

Construction of a Multiple Decrement Life Table .....................................................................

Construction of the Associated Single Decrement Life Table ...................................................

Differences Between Contraceptive Life Tables.........................................................................

Construction of a Multiple Increment Life Table ......................................................................

Methods of Counting .................................................................................................................

Summary ..................................................................................................................................

Notes .........................................................................................................................................

V. Summary of Pertinent Portions of the NSFG Qucstiontie ...........................................................

VI. Classification of Contraceptive Use Intervals by Contraceptive Intention............., .........................

Closed Pregnancy Intcwds ........................................................................................................

Open Pregnancy btcwds .......oo......oo.o.......oo..o..o........o..................o........o.......co......o.........o........o

VII. Contraceptive Failure Rates by Relative Age, Contraceptive Intention, Age at Last Live Birth,

Education, and Parity .....................................................................................................................

APPENDIX FIGURE

L Hyperbolas generated by equations 8 if qxl = 0.5 and qx2 = 0.2 ...................................................

38

38

38

39

39

39

40

40

41

43

48

49

49

50

51

53

55

55

56

56

58

60

60

61

62

57

LIST OF APPENDIX TABLES

I. Example of a simple muhiplc decrement life table with two dccrcmcnts ....................................... 52

IL Estimates of gross rates of discontinuation of contraceptive use (probability of discontinuation

of usc between months x and x + 1) for reasons 1 and 2, by method of computation...,, ................ 52

III. Estimates of gross rates of suMvrJ from reasons for discontinuation 1 and 2 (probability of not

discontinuing use due to reasons 1 and 2) to the end of the second month of USC,by method of

computation .oo.......o..o....o........o.o..o...o............o.........o..............o..............o.oo............................o......... 52

IV. Percent of married women 15-44 years of age who experienced a contraceptive failure during the

first year of USC,by relative age, contraceptive intention, age at last live birth, education, and

pqity: United States, 1970-73 ....................................................................................................... 62

37
APPENDIX 1

TECHNICAL NOTES

Background

This report is one of a series of statistical

reports based on information collected from a

nationwide sample of women through the National Survey of Family Growth conducted by

the National Center for Health Statistics,

The National Survey of Family Growth

(NSFG) utilizes a questionnaire to obtain demographic and socioeconomic information and information on fertility, family planning, and

health factors related to childbearing. As data

relating to various subjects within these broad

topics are ‘tabulated and analyzed, separate reports are issued, This report is based on data

collected in the first cycle of the survey.

The population covered by the sample for

NSFG is women 15-44 years of age living in

households in the conterminous United States at

the time of interview who were ever married or

had children of their own living with them. The

sample did not include women living in institutions or group quarters. Personal interviews were

conducted by the staff of the National Opinion

Research Center (NORC), Chicago, beginning in

July 1973 and ending in February 1974.

Statistical Design

The sampling plan for the survey was a

multistage probability design. Black households

and households of all other races were selected

at different probabilities so that the sample was

composed of about 40 percent black women and

60 percent women of all other races. The sample

was designed so that tabulations could be provided for each of the four geographic regions of

the United States.

of

38

The first stage of the

drawing a sample of

sample design consisted

primary sampling units

(PSU’S). A PSU consisted of a county, a small

group of contiguous counties, or a standard

metropolitan statistical area (SMSA) as defined

by the U.S. Bureau of the Census in March

1971. The second and third stages of sa!mpling

were used to select several segments (cIusters of

about 100 dwelling units) within each I?SU. A

systematic sample of dweI1ing units was then

selected from each segment. Each sample dwelling unit was visited by an interviewer, who listed,

all household members. If a woman under 45

years of age; ever married, or with offspring in

the household, was listed in the household, an

extended interview was conducted. If more than

one woman in the household met the eligibility

criteria, one of the women was randomly selected for an extended interview.

Since the design of NSFG was a complex

multistage probabilityy sample, the derivation of

estimates involved three basic operations:

Inflation by the reciprocal of the probability

of selection. –The probability of selection is the

product of the probabilities of selection from

each step of selection in the design (PSU, segment, listing unit, household, and sample persons within household).

Nonresponse adjustment. –The estimates

were inflated by a multiplication of two factors.

The first has the number of sample households

in a given PSU and stratum as its numerator and

the number of households screened in the PSU

and stratum as its denominator. The second factor has as its numerator the number of screened

households having an eligible woman of a specific age and race class and PSU group, and as its

denominator, the number of women actually interviewed in the same age and race class and

PSU. Screener response for the total survey was

89.8 percent and interview response was 90.2
percent for the total sample, yielding an overall

response rate of approximately 81.0 percent.

Poststratification by marz”ta[ status-agerace. –The estimates are ratio adjusted within

each of 12 age-race cells to an independent

estimate of the population for ever-married

women. These independent estimates were derived from the U.S. Bureau of the Census Current Population Surveys of 1971-73. The numbers of single women with offspring living with

them were inflated by the two steps just described.

All figures are individually rounded; aggregate figures are rounded to the nearest thousand.

The sums of aggregates and percents may not

add up to the total due to rounding,

The effect of the ratio-estimating process is

to make the sample more closely representative

of the population of women under age 45 years,

living in households in the conterminous United

States, and ever married or with offspring living

with them. The final poststratification reduces

the sample variance of the estimates for most

statistics.

Descriptive material on the sampling design

and estimation procedures may be found in

another report.6

Measurement Process

Field operations for the survey were conducted by NORC as agent for NCHS. The responsibilities of NORC included pretesting the

interview schedule, selecting the sample, interviewing respondents, and carrying out quality

control checks. The questionnaire was pretested

in November 1972 and subsequent smaller fieId

trials were held in March 1973. Interviewers

were trained for 1 week prior to fieldwork and

had their first few schedules reviewed thoroughly. During the first part of the fieldwork,

each interview schedule was reviewed for the

completeness of certain key items, and more

intensive review and followup were performed if

errors were discovered. Review and followup

were reduced to a sample of each interviewer’s

work in the later part of the fieldwork. A 10

percent sample of all households with telephones was recontacted to verify the interview

NOTE: A list of references follows the text.

and the accuracy of a fcw items. :\ll these ()p~rii.

tions were monitored by NCIIS.

Parts of the interview schcdulc applicable t()

this report are reproduced in appendix l’. ‘W

full questionnaire is reproduced in another

report.’ The complete schcdulcs arc muilablc on

request. Two different forms were used, onc for

interviewing currently married women and the

other for interviewing widowed, divorccci, separated, or single women with offspring living with

them. The two forms differ mainly in the worcling of items referring to the husband; there tire ;I

few questions in each schedule that CIOnot appear in the other.

Data Reduction

Coding and keying were done by NORC and

the U.S. Bureau of the Census. Each coder’s

work was systematically sampled for verification. Keying at the Bureau of the Census was

performed on key-to-disk equipment programed

to reject invalid entries. Each keyer’s work was

systematically sampled for verification. The data

were edited by the Bureau of the Census and

NCHS to minimize internal inconsistencies.

After editing, value entries were imputed to

cases with missing data on an item-by-item basis.

No item with more than 15 percent missing data

was included in the imputation. The imputed

value entry for a case was selected from a randomly chosen case with similar characteristics

such as race, age, and marital status, using a

procedure known as “hot deck” imputation.

Reliability of Estimates

Since the statistics presented in this report

are based on a sample, they may differ somewhat from the figures that would have been

obtained if a complete census had been taken

using the same questionnaires, instructions, interviewing personneI, and field procedures. This

chance difference between sample results and a

complete count is referred to as sampling error

and is measured by a statistic called the standard

error of the estimate. Approximate standard

errors for 1-year contraceptive use failure rates

reported in this study are shown in the lower

paneI of the detailed tables containing the rates.

39
These standard errors were’ computed using a

procedure known as balanced half-sample replication. Details of this procedure can be found in

another publication.G Standard errors for 2-year

use failure rates, continuation rates, and extended use effectiveness rates were not calculated because of time and cost considerations.

The chances are about 68 out of 100 that an

estimate from the sample differs from a value

that could be obtained by a complete census by

less than the standard error. The chances are

about 95 out of 100 that the difference between

the sample estimate and a complete count would

be less than twice the standard error. In this

report, percents that have a standard error that

is 25 percent or more of the estimate itself are

considered “unreliable.” The reader is advised to

use caution in interpreting results involving unreliable estimates.

In this report, sample statisticsare compared

among subgroups using the normal deviate test.

The level of confidence used with this test is a

matter of preference and in this case the 0.10

level was chosen. Thus a statistically significant

difference among comparable percents from two

or more subgroups is one sufficiently greater

than zero that a difference of that size or larger

would be expected in less than 10 percent of

repeated samples of the stie size and type if

there were no true difference in the populations

sampled. If the obsemed difference or a larger

one could be expected in more than 10 percent

of repeated samples, one cannot be sufficiently

confident to conclude that there is a true difference in the populations. When aq observed difference is sufficiently greater than zero to be

statistically significant, the true difference in

the population is estimated to lie between the

observed difference plus or minus 1.68 standard

errors of that difference in 90 out of 100

samples.

When two or more sample statisticsare compared and they have only small, statistically nonsignificant differences among them, they may be

referred to as the “same” or “similar.” However,

when a substantial difference observed is found

to be not statistically significant, one should not

conclude that no difference exists, but simply

that such a difference cannot be established with

NOTE: A list of references follows the text.

90 percent confidence from this sample. Observed differences that are described in terms

such as “greater,” “less,” “larger,” “smaller,”

and so forth, have been tested and found statistically significant. Lack of comment in the text

about any two statistics does not mean that the

difference was tested and found to be not

significant.

The standard error of a difference between

two comparative statistics, say, the proportion

of those with characteristic M among black

women compared with white women, is approximately the square root of the sum of the squares

of the standard errors of the statistics considered

separately.

A formula for the standard error of a difference, d =“P1 - P2, is

~d = <(P1 VP,)2 + (P* l+, )2

where PI is the proportion for one group, P2 the

proportion for the comparative group, and Vpl

and VP2are the relative errors of PI and”P2, respectively. This formula will represent the

actual standard error quite accurately for the

difference between separat: and uncorrelated

characteristics, although it. N only a rough approximation in most other cases.

Nonsampling Error

In addition to sampling error, the survey’

results are subject to several’sources of potential

nonsampling error, including interview nonresponse, nonresponse to individual questions

within the interview, inconsistency of responses

to individual questions, respondent error or misreporting, and errors of recording, coding, or

keying by survey personnel. It is impossible to

measure accurately the extent of nonsampling

errors. Although some useful approximate

measures can be made of some types of nonsampling error, the survey must rely on several

quality control procedures and other methods

incorporated into the survey design to minimize

nonsampling error.

Interview Nonresponse

Interview nonrtesponse, or the failure to

obtain whole interviews, arises from several

40
sources—incomplete listing of households for the

sampling frame, inability to screen dl sample

households for eligible respondents, and inability to complete a full interview. Completeness of listing cannot be tested directly because

it requires an independent, accurate accounting

of the households that should have been listed.

In NSFG, listing accuracy was tested at the time

of screening by use of the “half open interval”

check for missed households; that is, at designated sample households, the interviewer was

required to check for dwelling units between the

sample household just screened and the next

listed dwelling unit. This procedure resulted in

the addition of 781 missed units or an additional

2.4 percent to the origimd sample of dwelling

units to be screened.

Of the o;iginal” sample ‘of 32,818 dwelling

units to be screened, 3,820 were found to be

vacant, not dwelling units, or group quaxters. Of

the remaining dwelling units, 9.7 percent were

not successfully screened. This included 2.3 percent refusals to have the household members

listed; 1.6 percent of households with members

with language problems, illness, or otherwise

unavailable in the field period; 4.6 percent

where no one could be found at home; and 1.1

percent for other reasons such as refused access

to the unit.

Of the 26,177 households for which screening was completed, 10,879 were found to contain an eligible respondent. However, interviews

were not completed in 9.8 percent of these

cases because of refusals by the eligible respondents (5.0 percent); language, illness, and related

problems (2.0 percent ); and no contact after

repeated calls (2.7 percent).

The nonresponse adjustment for interview

nonresponse imputes to nonresponding, dwelling

units and women the characteristics of similar

respondent dwelling units.and women.

Item Nonresponse

Nonresponse to individual questions (item

nonresponse) was less than 2 percent for about

half (51 percent] of the items. Item nonrespomie

occurred when the respondent refused to answer

the question, when the respondent did not know

the answer to the question, when the question

was erroneously not asked or the answer not

recorded by the interviewer, and when the

answer was uncodable. For 37 percent of the

items, nonresponse was between 2.0 percent and

10.0 percent. For 12 percent of the items, nonresponse was greater than 10 percent for persons

eIigible to answer the items. Half of the high

nonresponse items were concentrated in two

areas-detailed income questions and questions

about the reasons for switching from one contraceptive method to another. The remaining high

nonresponse items were generally those asked of

small numbers of persons.

The amount of missing data or imputed

values for various items are shown with their

definitions in appendix II. Some illustrative

items and their nonresponse rates are: parity (no

missing data), intention to have another child

(0.7 percent), whether no contraceptive method

was used or contraception was stopped in order

to become pregnant (1.9 percent), and highest

grade of school attended (0.1 percent).

For most items an adjustment for missing

data was made by one of four imputation procedures. In order of frequency employed they

were: (1) “hot deck” imputation, (2) imputation from a sorted file, (3) editing from other

data within the same case, and (4) allocation

based on technical judgments.

“Hot deck” imputation refers to a procedure

in which the file is first randomized. Next a

matrix is created for values of items (e.g., race,

age, and marital status) judged to be correlated

with the item to be imputed (e.g., number of

times married). A reasonable “cold deck” value

(e.g., 2 = married twice) is assigned to each celI

of the matrix in case the first file record with

the given characteristics has missing data. The

randomized file is processed, and each record is

identified as belonging to one cell of the matrix

(e.g., white, aged 25-29 years, currently married). “The item to be imputed is checked: If it is

blank-not applicable (e.g., not married before),

it is ignored; if it has a missing data code, the

code in the matrix is placed in the record. If it

has an acceptable code, that code repIaces the

code already in the matrix, and it remains in the

matrix until another record with the same characteristics and a known code is encountered.

This ensures that the probabilityy of a code being

assigned to a record with missing data is the

41
same as the probability of that code occurring

among records with the same characteristics but

with known data.

For imputation from a sorted file, the

records are first sorted by selected characteristics (e.g., marital status,,race, and age) so that

the first group of records would be currently

,, married black women aged 15-19 years, the

second ~group would be currently married black

women aged 20-24 years, and so forth. AD initial

value is assigned fQr the item to be imputed—

that is, 4 (tubal ligation) ,for type of sterility,

and for any ‘item dependent on the item to be

imputed-for example, 9 (not ascertained) to

whether the operation was for contraceptive

reasons. The ordered, file is processed, and each

record is checked. If the item to be imputed is

blank–not applicable, it is ignored; if it has a

known code, the code replaces the existing set

of values; if the item has a missing data code, it

and its dependent items would be changed to

the preset values above. This procedure ensures

that the imputed code is reasonable for the

ordering characteristics and that the probability

of assignment is the same as that in the population in general. There is some bias, however, as

the boundaries between groups are crossed.

When sampling error affects the precision of

survey estimates, nonsampling error introduces

bias. Imputation procedures reduce this bias to

the extent that the assumptions about the relations between respondent and nonrespondent

characteristics are true. The amount of remaining bias, if any, cannot be measured. Therefore,

stringent quality control procedures were introduced at every stage of the survey, including the

check on completeness of the household listing

mentioned earlier, the extensive training and

practice of interviewers, field observations of

interviewers, field editing of questionnaires,

short verification interviews with a subsample of

respondents and missed households, verification

of coding and editing, an independent recoding

of a sample of questionnaires by NCHS, keypunch verification, and an extensive computer

“cleaning” to check for nonpermissible codes,

missing data, and response inconsistencies. One

source of bias that can be evaluated through

special studies but cannot be controlleci is respondent error, whether deliberate or unwitting.

In this survey as in others, the data are subject

to problems of accurate recall and the stability

of respondents~ views from one time to the

next.

Uuc)

42
APPENDIX II

DEFINITION OF TERMS

F%-egnancyinterval.–A pregnancy interval is

the period between marriage and the date of a

woman’s first pregnancy termination (regardless

of its outcome), or between the dates of two

successive pregnancy terminations (if she has

had more than one), or between the date of her

most recent pregnancy termination (or marriage

if she had no pregnancies) and the interview.

“ The latter interval is called the “open” interval,

because it has not been “closed” by a pregnancy; the others are “closed” intervals. Closed

intervzds are numbered from the earliest to the

most recent; the period between marriage and

the first pregnancy is the first interval, the

period between the first and second pregnancies

is the second interval, and so on. The first interval is only defined, however, when marriage precedes the first pregnancy termination. The dates

of pregnancies needed to define pregnancy intervals were obtained from each respondent as part

of her complete reproductive history. For the

sampIe as a whole, less than 10 percent of the

dates of pregnancy termination which determine

the first pregnancy interval are imputed because

of missing data. For all pregnancy intervals, the

proportion based on imputed dates decreases

with increasing pregnancy interval order.

Birth interval –A birth interval is the period

between marriage and the date of a woman’s

first live birth, or between the dates of two successive Iive births (if she has had more than one),

or between the date of her most recent live birth

(or marriage if she has had no live births) and

the interview. The latter interval is called the

“open” interval, because it has not been

“closed” by a birth; the other intervals are

“closed” intervals. Closed intervals are numbered from the eadiest to the most recent, in the

same manner as pregnancy intervals. Also,, the

first interval is only defined when marriage precedes the first live birth. The dates of births

needed to define birth intervals are obtained

from each respondent as part of the complete

history of her pregnancies. For the sample as a

whole, less than 10 percent of the dates of birth

which determine the first birth interval are imputed because of missing data. For all birth intervals, the proportion based on imputed dates

decreases with increasing birth interval order.

Contraceptive use intewal. –A contraceptive

use interval is the period between the date a

woman began the use of a contraceptive method

and the date she stopped using it (regardless of

the reason for stopping) or the interview date. In

addition, for the purposes of this study, only intervals that began during a marriage were considered. The dates of starting and stopping the use

of a method, needed to define contraceptive use

intervals, were obtained from each respondent

as part. of the history of her contraceptive use

between July 1, 1970 and July 1, 1973. Less

than 2 percent of contraceptive use intervals are

based on imputed data.

Contraceptive intention. –Contraceptive intention is the motive of the woman in using contraceptives. Women were classified into three

groups: “preventers,” those who used contraceptives to avoid any further (unwanted) births;

“delayers,” those who used contraceptives to

delay a wanted birth; and “indetermixxmt,”

those whose reasons for using contraceptives

were unclear. Women classified as “indetcrminant,” 10 percent of the respondents, were

omitted from the analysis. Contraceptive intcntion is based on imputed data for less than 5 percent of all respondents.

43
Contraceptive failure. –Contraceptive failure

is defined as having occurred if the woman becomes pregnant while using contraceptives.

Use failure rate.–A first-year use failure rate

is the percent of women who would experience

a contraceptive failure during the first year of

continuous contraceptive use. A second-year use

failure rate is the percent of women who would

experience a contraceptive failure during the

second year of continuous contraceptive use.

Both rates, as used in this study, are life-table

rates and thus represent the percent of a cohort

of women that would have experienced a contraceptive failure during the specified period if

the women had been subjected to the monthly

failure rates produced by the life table. The

monthly failure rates are based on the actual

experiences of the women in this study.

Use effectiveness rate. –First- and secondyear use effectiveness rates are the percents of

women who would not experience a contraceptive failure during the first and second years of

continuous contraceptive use, respectively.

These rates are equal to 100 minus the corresponding use failure rate.

Extended use failure rate. –A l-year extended use failure rate is the percent of women

who would experience an unintended pregnancy

within the first year after beginning the use of a

contraceptive method, regardless of whether use

was stopped before the pregnancy actually

occurred.

Extended use effectiveness rate.–A l-year

extended use effectiveness rate is the percent of

women who would not experience an unintended pregnancy within the first year after beginning the use of a contraceptive method, regardless of whether use was stopped during that

year. This rate is equal to 100 minus the l-year

extended use failure rate.

Continuation rate. –Twelve-, twenty-four-,

and sixty-month continuation rates are the percents of women who would continue to use the

same contraceptive method for 12, 24, and 60

months, respectively, after beginning its use.

Age at last live birth. –Age at last live birth

is the age, in years, of a woman at her lastbirthday before her most recent live birth.

Relative age.–Relative age is a classification

of the age of a mother at the time she gave birth

to a child of a given order, in relation to the ages

of all other mothers at the time they gave birth

to a child of the same order. For example, a

woman who had her first child at a very young

age, compared with other women, would be classified as having a “low” relative age for that

birth order. Relative age, in this study, is determined for each birth interval of the wornen in

the sample and is used to classify contraceptive

use intervals falling within each birth interval.

Patity. –Parity is the fact or condition of

having borne children and is specified in terms

of the number of live births a woman has had. A

woman with no live births is referred to in obstetrical and demographic terminology as “nulliparous” or “zero parity,” a woman with one live

birth is referred to as “primaparous” or “parity

one,” and so on. A woman’s parity was determined for this study from the questions, “Have

you given birth to a baby at any time?” and, if

yes, “Altogether, how many babies have you

given birth to, including any who died very

young?” The accuracy of this information is

further verified by obtaining detailed data about

each pregnancy and additional information on

pregnancies that ended in live issue. A complete

pregnancy history was a primary focus of the

survey, and information on the number of live

births and the number of pregnancies was obtained for 100 percent of the respondents,

Mafiiage cohort. –A group’ of women who

were first married in a specified calendar period

constitutes a marriage cohort. Because the information for classifying women in marriage cohorts comes from a sample at one point ill time,

it may be a biased sample of all women who

married in a specific period. Women who were

married in a specific period but who were outside the ages included in the sample, 15-44 years,

are not represented in the marriage cohorts constructed from these data. This bias is negligible

for recent cohorts but significant for earlier

cohorts ; in early cohorts, many women who

were of relatively advanced age at the time of

marriage were past age 45 at the time of interview and are not represented in the sample. The

effect of this omission is the overrepresentation

of early-marrying women in the early cohorts

constructed from the sample data. For that

reason, marriage cohorts earlier than 1955 are

not considered here.

Race. –Women were classified, as white,

44
black, or “other races” according to the interviewer’s observations at the time of interview.

The agreement between this classification and

the respondent’s own reports of ethnic origin,

also obtained in the interview, was very high; for

instance, of those classified as “black” by interviewer observation, 96 percent reported their

ethnic origin as at least partly “black, African, or

Negro”; of those who reported their ethnic origin as “black, African, or Negro,” 100 percent

were classified as “black” by interviewer observation. Race was imputed for 10 respondents.

Education. –Education was classified according to the highest grade or year of regular school

or college that was completed. The determination of the highest year of regular school or college completed by the respondent was based on

responses to a series ~of questions concerning

(1) the last grade or year of school attended,

(2) whether or not that grade was completed,

(3) whether any other schooling of a vocational

or generally nonacademic type was obtained,

and (4) whether or not such other schooling was

included in the years of regular school or college

reported in (1). Information on education was

reported almost completely: Only about 1 percent of the data was imputed.

Reli#”on. –Women were classified by religion

in response to the question: “Are you Protestant, Roman Catholic, Jewish, or something

else?” Because the numbers responding “Jewish” or “something else” were too few for separate analysis, and because those groups resemble

Protestants in their contraceptive practice, they

were combined with Protestants for this report

in a category “Other and none.” Data on religious denominations were reported for all but

26 respondents, or more than 99 percent. Religion was imputed for the 26 respondents.

Geoyaphic region, –For the purpose of classifying the population by geographic area, the

U.S. Bureau of the Census has grouped the 50

States and the District of Columbia into four

regions, as follows:

Rep”on States included

Northeast ............ Maine, New Hampshire, Vermont, Massachusetts, Rhode

Island, Connecticut, New

York, New Jersey, Pennsylvania

North Central...... Michigan, Ohio, Indiana, Illinois, Wisconsin, Minnesota,

Iowa, Missouri, North Dakota, South Dakota, Kansas,

Nebraska

South .................. Delaware, Maryland, District

of Columbia, Virginia, West

Virginia, North Carolina,

South Carolina, Georgia,

Florida, Kentucky, Texas,

Tennessee, AIabama, Mississippi, Arkansas, Louisiana,

Oklahoma

West .................... Montana, Idaho, Wyoming,

Colorado, New Mexico, Arizona, Utah, Nevada, Washington, Alaska, Oregon, California, Hawaii

Alaska and Hawaii are not included in the NSFG

sample design.

Place of residence. –The population residing

in standard metropolitan statistical areas

(SMSA’S) constitutes the metropolitan population. Except in New England, an SMSA is a

county or group of contiguous counties that

contains at least one city of 50,000 inhabitants

or more, or “twin cities” with a combined population of at least 50,000. k addition to the.

county or counties containing such a city or

cities, contiguous counties are included in an

SMSA if, according to certain criteria, they are

essentially metropolitan in character and are

socially and economically integrated with the

central county. In New England, SMSA’S consist

of towns and cities rather than counties. The

metropolitan population for this study is based

on SMSA’S as defined in the 1970 U.S. census

and does not include any subsequent additions

or changes. A more detailed discussion has been

published.s Place of residence was reported for

all respondents.

NOTE:A listof referencesfollows thetext.

000

45
APPENDIX Ill

SELECTION OF SAMPLE

For the calculation of “true” use effectiveness during the 3-year period prior to the survey,

all intervals of contraceptive use (including sterilization) occurring during a continuous marriage were considered. Certainly, many women

who are not married have intercourse and use

contraceptives, but their exposure to pregnancy

may be intermittent; therefore, their experience

was not considered.

The first step in the preparation of the data

for the calculations was the selection of eligible

intervals of contraceptive use. This process involved three steps: the elimination of ineligible

respondents, the elimination of ineligible pregnancy intervals, and the elimination of ineligible

intervals of contraceptive use (use intervals). All

numbers of women, pregnancy intervals, and use

intervals reported in this section are the raw unweighed totals. In all other sections failure rates

are based on the weighted observations. The

weight assigned to each respondent is a reflection of the type of multistage sampling scheme

employed by the National Center for Health Statistics (NCHS) to ensure that adequate numbers

of particular subgroups of the population, for

example, black women, were interviewed.

AU information for a respondent was

omitted if:

1.

2.

The respondent had not been marzied at

any time during the observation period

(1,635 women), either because the respondent was single on July 1, 1973

(742 women) or was widowed, separated

or divorced during the entire study

period, July 1, 1970 toJuly 1, 1973.

The respondent or her current husband

had become noncontraceptively sterile

before July 1, 1970 (324 women).

3. The number of pregnancy intervals ending between July 1, 1970 and JuIy 1,

1973 recorded in the pregnancy interval

data disagreed with the information

given on the 3-year chart of monthly

contraceptive status (75 women).

For the remaining 7,763 women, each of

their 10,865 pregnancy intervals falling at least

partly in the observation period was examined

and the pregnancy interval was disqualified if:

1.

2.

3.

4.

No method of contraception was used in

the pregnancy interval (2,474 intervals).

More than four methods of contraception were reported for a closed pregnancy interval. (The pregnancy interval

data allowed for the reporting of only

four contraceptive methods in any given

interval, precluding the possibility of

matching the information in the 3-year

chart) (1 interval).

Inconsistent or incomplete information

about the intention of sterilization was

recorded, or the date given for a contraceptive sterilization operation preceded

the date of termination of the last previous contraceptive method by more than

2 months (9 intervals).

There were discrepancies between the

pregnancy interval data and the information on the 3-year chart of more than 1

month in the date of the start (83 intervals) or the end (20 intervals) of a pregnancy interval. In cases in which the

pregnancy interval data showed a pregnancy lasting more than 10 months,

both the preceding and the following

46
5.

6.

7.

intervals (31 intervals) were invalidated.

In most such cases, it’ appeared that the

date of conception given in the pregnancy interval data was off by 1 year

and the 3-year chart had been adjusted

to show a pregnancy during the first part

of the time given. However, this adjustment often conflicted with other evidence in the record; thus it was not possible to determine the start and end of

gestation.

During a pregnancy interval overlapping

the start of the 3-year period, the number of months of nonexposure to the

risk of conception reported in the pregnancy interval data disagreed with information in the 3.year chart, and the

woman was married and using a contraceptive method on July 1, 1970 (275

intervals). In the absence of a month-bymonth record for the period prior to

July 1, 1970, it could not be determined

whether the period of nonexposure interrupted the period of contraceptive

use,

During a pregnancy interval overlapping

the start of the 3-year period, the

woman was already pregnant on July 1,

1970, so that no vflld contraceptive use

could occur in the pregnancy interval

(853 intervals).

Different pregnancies were recorded in 2

successive months so that there could,

according to the coding priorities, be no

record of intervening contraceptive use

(38 intervals).

Finally, within each of the remaining 7,081

pregnancy intervals, intervals of contraceptive

use were discarded if:

1. The respondent was not married at the

time contraceptive use began (595 intervals). For the pill and the IUD, use was

allowed to begin as many as 2 months

before marriage. There was no restriction

as to how long before marriage sterilization could have occurred, but exposure

to the risk of conception was considered

to begin in the month of marriage.

2.

3.

4.

5.

For contraceptive usc intends foll{>~~cd

in the same month by prcgnanc}”, it uvis

not known whether or not contraceptive

use was stopped before the pregnancy

began (67 intervals). Since this variahlc

was imputed, there should have been no

missing data, but in some cases the correct sequence of questions haci apparently not been asked. . .

For contraceptive use intervals followed

by pregnancy, there was a discrepancy

between the pregnancy interval data ancl

information on the 3-year chart as to

whether contraceptive use was stoppccl

before the pregnancy began (34 intervals).

The contraceptive method reported M

being used at the start of observation

(July 1, 1970) on the 3-year chart was

not the same method as the one reported

for that date in the pregnancy interval

data (68 intervals).

The contraceptive method was not ilcceptable (essentially noncontmceptivc

sterilizations that were entered on the

3.year chart) (15 intervals).

An additional 588 contraceptive use intervals were, in effect, discarded because reproductive intention could not be determined. The 588

contraceptive use intervrds of indeterminate intention were not incIuded in any tabulation.

Since to be classified as having indeterminate intentions in a closed interval implies a marital disruption, and hence excIudes the possibility y of

observing a contraceptive failure, and because all

open intervals so classified are contributed by

women who are post-married, sterile, or for

whom pregnancy is medically inadvisable, a classification of indeterminate does not represent a

category of intention between prevent ~and

delay.

lt is difficult to speculate with any degree ot

certainty about the effect of the large number

o.f data exclusions. We suspect that, on”balance,

respondents excluded are the relatively less successful contracept~rs and that, as. a consequence,

the failure rates presented here may be somewhat low. Also, if the 101 contraceptive use in47
tervals excluded for reasons 2 and 3 included a this hypothesis, since the vast majority of exclularge number of contraceptive failures, their ex- sions were made because of inaccuracies in the

elusion biases further downwards the rates pre- data that could not be resolved.

sented here. However, it is not possible to test

000
APPENDIX IV

THE CALCULATION OF GROSS RATES OF CONTINUATION FOR

CONTRACEPTIVE METHODS: SINGLE AND MULTIPLE INCREMENT LIFE

TABLES

James Trussell and Jane Menken

A decade ago,

biases involved in

Robert Potter, realizing the

using the Pearl index as a

measure of contraceptive effectiveness, proposed

analyzing contraceptive continuation by lifetable procedures.g Many such life tables have

now been prepared by various researchers,1*10-19

and the recent development of FORTRAN pro-

~ams for (mini-) computers drastically eased the

manipulation of great quantities of data and

facilitated computation.16 Moreover, the Population Council, in collaboration with Potter, has

issued a series of recommended programs for

evaluating continuation rates.1‘~18 The purpose

here is to point out a logical error in the accepted method for constructing the single decrement life table associated with the multiple

decrement life table, generated by competing

reasons for stopping contraceptive use, and to

propose an alternative derivation of these gross

rates.k Moreover, a different procedure is recommended for handling women who are lost to

foIlowup or are censored by the initiation of the

analysis. The first two sections of this appendix

contain a review of the procedure for constructing a single and multiple decrement life table

NOTE: A list of references follows the text.

‘This treatment is a simplified version of Chiang’s19

mathematical exposition of competing risks. It differs in

that the assumptions are modified somewhat to take

into account specifics of the contraceptive use situation.

Because much of this mathematical literature on competiug risks is inaccessible to most demographers, the

method is derived simply in detail in this appendix.

and may be omitted by those familiar with the

standard notation and methodology.

Preliminary Manipulation of the Data

The procedure developed by Potterz” for

analyzing the continuation of IUD use in Taiwan

is quite generaI and can be readily adapted for

analyses of other methods and for use in situations other than cIinical trials. Each woman,

after insertion of the IUD, is observed at regular

intervals and is recorded at each observation as

being in a certain status (continuing use, expulsion, pregnant, etc.) in an ordinal month of use.

For example, a woman maybe recorded asbeing

a continuing user in”the 6th month or as having

expelled her IUD in the 12th month. Such an

accounting procedure is used in medical clinics;

the patient fde contains this information. Next,

at the time of the analysis, women are ckssified

by their terminal status. Normally the first segment of use of a contraceptive is the segment

of interest; this segment can be terminated by

pregnancy, other discontinuation, loss to followup (LFU)} or by the initiation cif the analysis itself (the. woman is stiIIusing contraceptives

at the time of the analysis). It is very important

to note that if a woman is lost to followup, she

is coded in the terrnkxd status LFU in the

nwnth or her last contact with the chic, not

10f course, there were no c&es lost to followup in

the NSFG data. This terminal category is included here

for completeness.

49
the month in which she was sought but not

found. Similarly, pregnancy should be coded in

the month in which it occurs, not in the month

in which it is confirmed. However, since pregnancy cannot be detected in the month in which

it occurs, problems arise; these are discussed in

the last section of this appendix. Next, the

length of observation from initiation to terminal

status is measured. Since the length of observation is measured in ordinal months, a procedure

for computing the number of women retaining

the IUD at the start of the monthly interval is

necessary,

As an illustration, the case in which observation is measured in intervals of 1 month was

chosen. Other intervals, such as 3 or 6 months,

are permissible, and the methodology is unaltered, The notation used by Potter is very convenient:

N% =

Dxj =

T% =

F% =

c% ‘

number of women retaining the. IUD

at the start of the monthly interval

(x, x + 1), i.e., the (x + l)th ordinal

month;

number of terminations during month

(x, x +1) due tocausej;

2Dxj = total observed terminations

i during month (x, x + 1);

number of women lost to followup

during month (x, x + 1);

number of continuing users last observed during month (x,x + 1).

The terminology “in month x” refers to experience in the ordinal month x + 1. Note that this

treatment is identical with common usage of the

concept of age; children aged 4 are in their 5th

year of life.

Since the only known quantities are the

number of insertions (N.), the number of terminations observed in month x, (TX), the number

of continuing users last observed in month x,

(CX), and the number of women lost to followup

in month x, (Fx ), ATx+1 must be obtained recursively:

NX+l=NX-TX-FX -C’ %20. (1)

By such a procedure, a preliminary table, which

shows NX, CX, T%,and Fx, is obtained. One more

modification is needed before a life table can be

computed. The value N% is not, properly, the

number of women who are exposed to the risk

of terminating use. Women coded as both Fx

and C’ are included as exposed to risk for a full

month. However, since they have been observed

for, on the average, only half a month, Potter

removed one-half month for each of these

women to obtain the adjusted number of

women entering month x:

~ =Nx -Yz(FX +Cx). (2)

This procedure is in keeping with the “standard

assumption that cases lost to followup are unselected relative to the sub sample effectively observed during that month. Women whose experience is censored due to the initiation of the

analysis and women who are lost to followup are

treated in the same way, because there is no

chance of observing a termination; the observation of both types of women is artificially ended

by an event that is not a proper cause of methcid

termination, It is suggested later that the two

types of termination should be treated differently,

Construction of a Multiple Decrement

Life Table

The construction of a single decrement table

can proceed in the usual manner once the initial

data manipulation has taken’ place. Let the conditional probability of failing during the xth

month (the interval x to x + 1) be qx; then qx is

estimated in the Potter procedure by

(3)

and the estimated probability of retaining the

device for exactly x months is given by

fx=:fr-- (1 - $t). (4)

The discontinuation rates by individual

cause in a multiple decrement life table, called

“net rates” by Tietze, are similarly constructed.

If we let qxj be the conditional probability of

50
failing during the xth month due to cause j, then

9xj’s ‘Stimated bY

Dxj

9X =—

A?;

(5)

where Dxj is the number of discontinuations due

to cause j in month x. The cumulative rate by

duration x of discontinuation due to cause .i

((&j) is

x-1

Qxj = ~zO= ‘tqtj, (6)

which can be estimated from the $X and ~xj.

Further, it is clear that the sum of cumulative discontinuation rates by cause equals the

cumulative discontinuation rate for all causes;

‘hence, the cumulative discontinuation rates are

additive.rn

Construction of the Associated Single

Decrement Life Table

The cumulative discontinuation rates due to

cause j in a multiple decrement life table are

functions of the other competing discontinuation rates. As Potter9 explained:

<c

. . . a problem arises when net cumulative

rates are used in comparing the relative frequency of a particular type of termination,

such as expulsion, in two different samples

or in subgroups within a sample. For example, suppose that the monthly rates of

expuIsion—that is, the probabilities of expelling during the first month after insertion,

the second, and so on–are lower in sample B

than in sample A for those retaining the device up to the beginning of that month.

Now, if the levels of competing risks are also

lower in B than in A, so that fewer women

in B are lost to pregnancy and removal and

‘:Qxj = ;>: Pt%j=>j%j =~; Ptqt = Qx. .

i

AU tke rates~can be replaced by keir estimators to obtain Z&j = Qx.

i

therefore more women are exposed on the

average longer to the risk of expulsion than

is the case in A, then it is possible for sample

B to show a higher net cumulative rate of expulsion despite its lower monthly rates of

expulsion. ”

Therefore, it is enlightening to construct a life

table in which all competing risks other than the

one(s) of interest have been eliminated. Preston

et al.,zl in their work on cause of death, called

such a life table the associated single decrement

life table. Tietze labeled the rates calculated

from the associated life table “gross rates.” Suppose that we are interested in cause j; then all

the other causes we seek to eliminate can be denoted ~ Further, associated life-table risks are

indicated by an asterisk over the rates. Then it is

clear that the cumulative rates in the associated

tables must satisfy one constraint:

(7)

In words, at duration x the product of the

probability of continuing contraceptive use if

cause j is the only cause of discontinuation and

the probability of continuing use if only cause j

is eliminated must equal the observed probability of continuing use if all causes are considered together. At duration x the cumulative net

failure rates are additive and the cumulative

gross continuation rates are multiplicative over

all causes.

We denote by q~j the gross rate of discontinuing in month x from cause j when all other

causes are eliminated. Pot ter’s procedure for

estimating the q~j is a direct extension of the

method for estimating the net rates given by

equation 5. It consists of subtracting from A&

one-half the number of women who discontinued contraceptive use for all causes other

than the one under consideration on the grounds

that, on the average, they would have been exposed to the risk of discontinuation of use for

the cause of interest for about half a month.

This procedure, however, only approximates the

constraint (equation 7), as seen from the example discussed later and demonstrated in

tables I-III. However, an exact computation of

risks that satisfies equation 7 can be easily developed.

51
Table 1. Example of a simple multiple decrement life table with two decrements

Number of

Adjusted women who

number of discontinue Observed proporwomen still contraceptive tion discontinuing

Month of use using a con- use for rea- use for raasons

traceptive at sons 1 and 2 1 end 2 between

the beginning between months x and x + 1

of month x months

xandx+l

x .................................................................................................................. Nx ‘ Dxl DX2 4X, 4X2

o.................................................................................................................. 1,000 100 200

1

0.1000 0.2000

................................................,,..............................................................,, 700 100 100

2

0.1429 0.1429

................................................................................................................,. 500

Table 11, Estimates of gross rates of discontinuation of contraceptive usa (probability of discontinuation of use between months x and

x + 1) for reasons 1 and 2, by method of computation

Method of computation

I Formula 9 ] Potter procedure

Month of uw Probabilities of dis- Probabilities of discontinuing use for continuing use for

reasons 1 and 2 reasons 1 and 2

between months between months

xandx+l xandx+l

x ................................................................................................................................ ....... I

ail

I

$jz I & [ 4;2

o ...................................................................................................................................... . 0.1118 0.2118 0.1111

1-

0.2105

1 ...................................................................................................................................... . 0.1548 0.1548 0.1538 0.1538

Table II 1. Estimates of gross rates of survival from reasons for

discontinuation 1 and 2 (probability of not discontinuing

use due to reasons 1 and 2) to the end of the second month

of use, by method of computation

Method of computation

Formulas 9 and 11

I

Potter procedure

and formula 11

Probabilities of not Probabilities of not

discontinuing use discontinuing use

for reasons 1 and 2 for reasons 1 and 2

by the end of by the end of

month 2 month 2

)$1 $;2

I

$;, )32

0.7506 0.6661 0.7521 0.6680

52
Let us consider two possible causes of discontinuation of contraceptive use. We need

never consider more than two at one time, since

we can combine all causes into the cause(s) of

interest and the cause(s) we wish to eliminate.

In the population (the multiple decrement lifetable population) the net rates are qx~ and q%~

and the gross rates are qjl and q; z. Then we can

express the qx~in terms of the q.$ias follows

9.1 = P;29;1 + %$29;1 = 9;1 (P:2 + %:2)

(8)

9X2 = P;l 9;2 +Wl 9;2 = 9;2@;l +%?:1)

where

and the simplifying assumption is made that if

both causes of discontinuation occur in the same

month x it is equally likely that cause 1 precedes

cause 2 and vice versa. In words, the expected

proportion of women who discontinue use because of cause 1 is equal to the probability of

dkcontinuing use because of cause 1 if it alone

operated times the expected proportion of those

who would be at risk if came 2 alone operated

(those who would continue and half those who

would discontinue). The statement for cause 2 is

symmetric.

Solving for q~l, we obtain

2+%C1-9X2W (2 +qxl -qx2)2 - 8qx1

9;1 =

94

(9)

Formula 9 is obviously symmetric for qj2.

Further, it can be shown (see the notes that

follow) that the expressions under the radical

for both q~l and qJ2 are equal. Since equation 9

yields two values of q; ~, how do we know

which one to choose? First, it is clear that qj ~

must be bounded by the constraint

since the women who discontinue use for cause

2 do so somewhere between the very beginning

(upper bound) and the very end (lower bound)

of month x. Second, it is shown in the notes

that follow that only one root will lie within the

bounds set by equation 10 provided that

that is, provided that the qx in the single decrement life table is less than 1 for any given

month. This condition must always be satisfied;

moreover, the root computed by subtracting

the expression under the radical in equation 9 is

always chosen. Estimates of the q.ji are obtained

by replacing the qxi’s in equation 9 by their

estimates, the 4X~’s.

Now that the framework of analysis has

been fully explored, let us turn to the example

given in table I. From the first three columns of

table I, the values of ~xi given in columns 4 and

5 are first computed. The values of ~Ji can be

computed according to equation 9. These estimates, along with the estimates of the q*’s obtained from the Pott~r procedure, are shown in

table II. Finally, the P~i can be constructed by a

procedure analogous to equation 4:

A* P2i = Ni ● i%” (11)

These estimates are presented in Jable II.

Using equation 7, the product of PJ1 by J~2

in table III should be 0.5, the proportion of

women continuing use to month 2 in the multiple decrement life table; the };. computed according to equations 9 and 11 satisfy this constraint, but those computed according to the

Potter formula do not. In this example, the

product from the Potter procedure is 0.502 and

the bias is quite small. However, as the number

of types of termination or the number of

months of followup increases, the biases can

become large.

Differences Between Contraceptive

Life Tables

The fact that pregnancy cannot be detected

at the time it occurs poses a serious problem in

the treatment of women whose experience is

censored by either the end of observation or 10SS

53
to followup. To a first approximation, expulsions and removals of IUD’s for pain and/or

bleeding occur uniformly over a cycle, and they

can be observed when they occur. Hence, we can

be sure that the CX women who were observed

to be continuing IUD users of contraceptives of

duration x months at the time of the study had

not in fact expelled the IUD or had it removed.

We cannot be sure without further followup,

that they were not pregnant at that time. Therefore, unless all women classified as CX can be

located approximately 2 months following the

close of the study and be found to be not pregnant, their full observed period of exposure

cannot be utilized in the construction of any life

table. Instead, only the segment for which a

pregnancy could possibly be observed can be

used. We suggest that an arbitrary 2 months be

subtracted for all CX women. By this procedure,

all CX women are either coded or recoded as

$..2. By the same logic no observed termz’natton should be recorded during the last 2 months

of the study. Women who conceive during this

period should be coded as continuing users in

the 3d month prior to the close of the study.

This procedure with regard to continuing users is

equivalent to Tietze and Lewit’s recommendation 8 of establishing the cutoff date for a study

at least 2 months before the calendar month of

analysis,n Also, records of women who are followed for less than 2 months must be discarded

entirely, Unless such a procedure is followed,

some pregnancies will be missed and all rates

(single decrement, gross, and net) will be biased

downward.

Women who are lost to followup constitute

a different problem entirely. There are three

choices of treatment of these cases:

1. Code these women as last observed at

month x. This is the treatment proposed

by Potter and by Tietze and Lewit. By a

logic identical to that above, however,

we do not know that these women were

not already pregnant at month x. Hence

the net pregnancy rates in month x or

‘They do not, however, consider any of the problems

discussed below which

women lost to followup.

arise from their treatment of

2.

3.

x -1 will be biased downward, and the

other net termination rates will be

slightly biased downward, since some

pregnant women would be erroneously

included in their denominator.

Code these women as last observed at

month x -2, that is, treat them the same

as women censored by the end of the

study at month x. In this case, the net

pregnancy rates are unbiased, but all

other failure rates are biased upward

since months of exposure are taken from

their denominator.

Treat loss to followup as a competing

risk. This treatment - is propos~d b~

Chiang, but it has the obvious clisadvantage that this risk includes pregnancy,

since some women who are lost to followup are pregnant.

This discussion emphasizes that there is no

unambiguously correct way to handle women

who are lost to followup. However, if our primary concern is the estimation of pregnancy

risks, alternatives (1) and (3) are obviously unsatisfactory. We are left with alternative (2);

clearly, even though the multiple decrement

pregnancy rates will be correct, the gross pregnancy rates will be affected if loss to followup

accounts for a significant proportion of all terminal codes.

Given these decisions, women who are last

observed at month x (either censored or lost to

followup at x) can be assumed not to be pregnant at month x -2. Because it is certain that

they did not terminate contraceptive use for any

other reason, it can be assumed that they are observed for the full month x -2.0 Therefore,

equation 2 must be modified to be identical

with equation 1.

N:+ ~ = Nx+l =NX-TX-FX-CX x’> (j

(12)

0 Equivalently, if all women can be located 2 months

after the close of the study, each can be given a full

month of exposure in month x.

,54
with the understanding that women censored or

lost to followup at month x are coded as CX.2

and Fx _2, respectively.

Construction of a Multiple Increment

Life Table

The preceding discussion holds for situations

in which it is possible to follow women from the

time of initiation of contraceptive use to the termination of use or the beginning of the analysis.

In many cases such prospective studies are not

possible. Instead one observes for some time

period a cross-section of women who have been

using contraceptives for various durations. The

methodology developed above would enable one

to analyze only the experiences of women who

initiated contraceptive use during the period

under observation. If this period is short, then,

on the average, the subsample of women initiating use would be small in relation to all users.

Furthermore, any life table constructed must

terminate at a duration that does not exceed the

period of observation.

The construction of a multiple increment

life table allows all period use to be considered.zz First each woman is coded both by terminal status (TX, Fx, or C%) and by the month of

use in which she entered into observation Ey

where y G x.P

The experience of a woman who enters observation at month y is counted in the life table

only at months > y. Her (successful) experience

before month y is not counted, since women

who started to use contraceptives at the same

time but failed before month y are not observed

and their experience is not counted. The assumption underlying the construction of a multiple increment life table is that women who

enter observation at month y are representative

of all women who are still using contraceptives

at month y. The only change in methodology

occurs in the recursive formulation of N;:

N; = tiEo (13)

PActually, y < x -2 if the terminal status is F’ or

Cx, since Fx and C! will be recoded as FX.2and C’-2.

N;= Eo-To-Fo -Co +-El (14]

N*X+1 =NX-TX- FX-C’X+L’. +I (15)

where it is understood that women censored or

Iost to followup in month x have been rccodcd

as CX-2 and Fx -2, respectively. Furthermore, no

woman who enters in month y and terminates as

FX-2 or C’-2 is counted unless x -2> y. The

Y2E0 arises because the first month of use within

the period of observation is considered to have

contributed half a month of exposure on the

assumption that initiation occurred halfway

through the calendar month. However, women

who enter observation in month x, Ex, are observed for the full month x during the first calendar month of the study.

Methods of Counting

It should be pointed out that the different

treatment of exposure attributed in the first

month is due to a different method of counting.

In prospective studies, the counting normally

takes place from date of initiation (insertion of

an IUD), and the unit of measure is an ordinal

month (from January x to February x). In the

partially retrospective studies, for which a multiple increment life table is appropriate, the unit

of counting is normalIy a calendar month (i.e.,

June, July, August). If the unit of counting in a

prospective study is a calendar month, the same

rule of a half-month of observation in the first

month should be followed. Perhaps an example

will make this point clearer. A woman has an

IUD inserted on January 15 and is estimated to

have become pregnant on July 5. If counting

takes place in ordinal months from January 15

then she contributes 1 month of observation in

the month of insertion (January 15-February 15)

and 6 months of observation in all (January 15-

JuIy 15). If the unit of counting is a calendar

month, the woman contributes half a month in

the month of initiation (January) and a total of

6% months. On the other hand, if pregnancy had

occurred on July 20, the ~ordinal method of

counting would have given 7 months of observation, but the calendar method only 6%. Therefore, both methods lead to the same estimates,

on the average. It is cIear that the ordinal

method is preferable because it is more accurate,

55
but the calendar information is much easier to

collect; the data for the 1973 NSFG were coded

using the calendar method.

Summary

We have proposed a method for coding

women lost to followup and women whose experience is censored by the initiation of a study

so that better estimates of terminations of contraceptive use due to pregnancy can be calculated. It must be emphasized that net pregnancy

rates are unbiased only if loss to followup and

pregnancy are independent. If women are lost to

followup because they are pregnant, failure rates

will certainly be biased downward. No valid assumption regarding nonindependence can be

made, however, unless the true status of women

lost to followup is known, in which case the

problem is irrelevant, since they are no Ionger

lost to followup. Nevertheless, the assumption

of independence is a strong one “andmay not be

valid.

In addition, we have suggested a procedure

for calculating the associated single decrement

contraceptive use failure rates which satisfies the

fundamental constraint that the associated single

decrement rates replicate the proportion of

women still using contraceptives after a given

duration of time in the multiple decrement life

table. This method admittedly involves a greater

number of numerical calculations than does the

Potter formula; however, since most analyses are

performed with the aid of an electronic computer, this consideration is of little importance.

Notes

It can be shown straightforwardly that the

procedure outlined previously will yield an extraneous root in every case of interest. From the

previous discussion we know that q; ~ must be

bounded by the constraints

9x 1

qxl < q;l < —

l-qx2’

(Al)

where

2+9X1-9X24 (z +qxl -qx2)2 -aqxl

9;1 =

.

9

(AZ)

Since the expression under the radical equals

% = 4(1-9X1 -%2)+(%1 -9$c2)2 (As)

and since

9X = 9X1 +9x2 < 1> (A4)

then all roots are real. The reformulation of the

expression under the radical as equation A3

leads to a computational saving when calculating

qJ2. Equation AZ is obviously symmetric for

q~2, and, since the interchange of second subscripts in equation A3 does not alter the value of

Rx,then

2+9X2 -!IX1

& R?$

d2 =

(A5)

2

We are faced next with the apparent choice

of two possible values of both qj 1 and q: z. We

can gradually narrow the range of choice. First,

the hyperbolas equation (8) are re-expressed in a

way that makes the asymptotes evident:

()9%1

!7:2 =21-—

d 1

()%2

!?; 1 =21 .—O

d 2

(A6)

These two hyperbolas intersect only twice, as

shown in figure I, so that we are left with a

choice of either both smaller or both larger

values of the q*’s obtained from equations AZ

and A5. Next, we note that equation A4 implies

that the upper limit for q; 1 given by equation

Al is less than 1. Therefore, if it can be proved

that, the greater value of qj ~ given by equation

M is always gyeater than or equal to 1, then the

solution to equation A6 given by the larger pair

of values will always be extraneous. For a given

value of qx,

2+%1 -9X2 + Z&

9:1 =

(A7)

2

56
2,0r

1.6 -

1.2 - % -0.5

&

.8 -

.4 -

.2.0 -1.6 .1.2 -.8 -.4

-.4 -

..6 -

-1.2 -

.1,6 -

-2.0 -

-2.4 -

-28 -

Figure 1. Hyperbolas generated by equations 8 if qxl = 0.5 and

rxz = 0.2

2+qx2-9xl - lp .

9:2 =

2

(A9)

Finally, we must show that the values given by

equations A8 and A9 satisfy equation Al. Figure I demonstrates that both pairs of roots satisfy the constraint that q~i > qx~ as follows

from equations A8 and A9. Next we let q~l be

larger than the upper boundary of equation Al.

9X1

9;1 ‘ — wherek > 1. (A1O)

1 -kqx2

Then by substituting qjl from equation A1O

into the first equation in A6, q~2 = 2kqx z; from

the second equation in A6, we see that qj 1 must

then equal 2(1 - l/2k), which implies that

9;1 > 1“ Butt bY an WWment similar to the

one used above, it can be shown that the maximum value of equation A8 is qx < 1 when

9X1 = 9X “ A symmet~c arwent holds for 9;2 $

and the proof is complete.

Fimdly, from equations A8 and A9 it can be

shown that

reaches a minimum value of 2 - 9X > 1 when

9X 1

= O. Therefore, when condition A4 holds, 41 “ P;2 = 1-9X1 -9%2 the value of q;, given by equation A7 will

-----

always be greater than 1. ‘The-same

holds for the larger q~2 vzdue. Hence,

pair of roots is extraneous, and ~%

subtracted to obtain the correct root:

argument

the larger

is always

(A8)

—o

=~-qx

‘Px” (All)

Formula Al 1 in turn guarantees that constraint

(equation 7) wiIl be met.

00

57
APPENDIX V

SUMMARY OF PERTINENTPORTIONS OF THE NSFG QuEsTlONNAIRE

Question

no.

Question

no.

For all currently married respondents:

11 ...........Date of current marriage (me., day,

yr.)

For all post-married respondents and

respondents mawied more than once:

12........... Date of first marriage

,. 13............ How marriage ended

14 ...........Date of divorce/death

–If marriage ended in divorce:

15 ...............Date stopped living together

For all respondents with any live

births:

19A ........Date of each live birth

For all respondents:

23 ........... Are you currently pregnant?

–If don’t know,

Do you think you probably are

., or probably aren’t ?

24,25,26 ..... Dates of all pregnancy terminations

other than live births

For each closed pregnancy interval

ending on or af~erJuly 1, 1970:

36 ........... Periods of no intercourse

37 ........... Did you use any method of contraception?

38 ........... List methods

For each method:

39 ................... Date started using

40 ................... Did you skip using (often,

sometimes, only once or

twice)?

Interviewer then reviews 3-year history with respondent, filling out 3-year month-by-month chart

of contraceptive status.

41 ...................Date stopped using

42 ...........when did you become pregnant?

–If stopped using last method same

month became pregnant:

43 ...............Had you stopped using (METHOD) before becoming pregnant?

–If yes to q. 43 or stopped using

before month of conception:

44 ...............Was the reason you stopped because you, yourself, wanted to

become pregnant?

45 ...........At the time you became pregnant

did you, yourielf, actually want

a(nother) baby sometime?

Is that how you felt before you became pregnant or did you come to

feel that way later?

–If “yes” to q. 45:

46 ...............Did you become pregnant sooner

than you wanted, later than you

wanted, or just about the right

time?

For open pregnant y interval:

49 ...........Periods of no intercourse

50 ...........Did you use any method of contraception?

51 ...........List methods

For each method:

52 ...................Date started

53 ...................Did you skip using (often,

sometimes, only once or

twice)?

For each method except last:

54 .“.................. Date stopped

For last method:

55 ................... Still using?

58
Question Question

no. no.

For all respondents who have not previously mentioned sten”lity:

57 ...........Do you have any reason to believe

it would be difficult or impossible

to have a(nother) baby?

58 ........... Reason it would be difficult or impossible

For all respondents for whom pregnancy is judged to be impossible:

59A ........ Type of operation or accident, illness, unspecified

59B ........ Date of operation/learned of sterility

For operations:

59C .................Was operation at least partly

so that you would not have

any (more) children?

For all respondents for whom pregnancy is judged possible and who are

either currently marn”ed or who expect remarn”agejreunion:

67 ...........Do you and your husband intend to

have a(nother) baby?

–If don’t know, disagree, etc.:

73A ............ Smallest number you expect to

have

73B ............ Largest number you expect to

have

NOTE: The interval file is constructed from responses to questions 19A, 24-26, and 36-55. All other information is

contained in the respondent file.

000

59
APPENDIX VI

CLASSIFICATION OF CONTRACEPTIVE USE INTERVALS BY

CONTRACEPTIVE INTENTION

A contraceptive use interval is any period of

exposure to the risk of conception during which

a woman was both married and using a method

of contraception. Periods of exposure to the risk

of conception that began prior to marriage were

excluded. A contraceptive use interval was classified as a delay interval if the woman’s motive

for using a contraceptive was to delay her next

pregnancy. If her intention was to have no more

children, the interval was classified as a prevent

interval. If the woman’s intention at the time of

contraceptive use could not be determined, the

classification was indeterminate. Since all tabulations were separated into prevent and delay categories, indeterminate intervals were excluded

from the analysis. Most indeterminate intervals

were contraceptive use intervals followed by

marital dissolution within the same pregnancy

interval; the woman’s intention during such an

interval could not be deduced from her responses to questions pertaining to the end of the

pregnancy interval (either conception or interview). In addition, women who were either sterile or for whom future pregnancies were ruled

out for medical reasons were not asked their reproductive intentioh; thus their intention during

the open pregnancy interval for methods other

than contraceptive sterilization could not be

determined.

The classification pertained only to pregnancy intervals ending after July 1, 1970 and to

women who were married contraceptive users

during part or all of the interval. The classification,was determined in the following manner:

Closed Pregnancy Intervals

Women who answered “no” to q. 37

(.. . This interval, did you ever use any method

to delay or prevent a pregnancy?) or who were

not married at any time during the pregnancy interval were not considered.

Delay

(A) 1.

2.

3.

4.

“Yes” to q. 44 (Was the reason you

. . . stopped . . . because you wanted

to become pregnant?) or

“Yes” to q. 45 (At the time you became pregnant . . . did you want to

have a(nother) baby at some time?)

and “before” to q. 45A (. . . is that

how you felt before you became

pregnant or did you come to feel

that way later?), or

“No” to q. 45 and “later” to q.

45B (same as 45A), or

“Don’t know; don’t care” to q. 45

and “probably yes” to q. “45C

(probe), and

(B) The marriage during which contraceptive use occurred was intact at conception.

Prevent

(A)

(B)

1. “No” to q. 45 and “before” to q.

45B, or

2. “Yes” to q. 45 and “later” to q.

45A, or

3. “Don’t know; don’t care” to q. 45

and “probably no” to q. 45C, and

The marriage during which contraceptive use occurred was intact at conception.

60
Indeterminate Prevent

The marriage during which contraceptive use

occurred dissolved before conception.

Open Pregnancy Intervals

Women who answered “no” to q. 50 (Since

your last pregnancy/July 1, 1970, did you ever

use any method to delay or prevent a pregnancy?) or who were not married at any time

during the pregnancy interval were not considered.

Delay

(A) 1. “Yes” to q. 76 (Is the reason you

are not using a method . . . because

you . . . want to become pregnant

as soon as possible?), or

2. “Yes” to q. 67 (Do you and your

husband intend to have another

baby?), or

3. “Don’t know” to q. 67 and

“greater than zero” to q. 73 (Many

peopIe aren’t sure but . . . what is

the largest number of (additional)

babies you expect to have?), and

(B) The marriage during which contraceptive use occurred was intact at interview.

(A) 1.

2.

(B) 1.

2.

a. “No” to q. 67, or

b. “Don’t know” to q. 67 and

“zero” to q. 73, and

The marriage during which contraceptive use occurred was intact at

interview, 07

“Yes” to q. 59C [was the (sterilizing) operation done at least

partly so that you wouId not have

(more) children] , and

The method under consideration is

contraceptive sterilization.

Indeterminate

(A) 1.

2.

Q. 67 not asked (woman is either

separated, widowed, or divorced

without marital expectations or

pregnancy is impossible or ruled

out for medical reasons), or

Marriage during which contraceptive use occurred is not intact at

interview, and

(B) The method under consideration is not

contraceptive sterilization.

ooo —

61
APPENDIX Vll

CONTRACEPTIVE FAILURE RATES BY RELATIVE AGE, CONTRACEPTIVE

INTENTION, AGE AT LAST LIVE BIRTH, EDUCATION, AND PARI”TY

Table IV. Percent of married women 1 I 5.44 years of age who experienced a contraceptive failure during the first Year of use, by

relative age, contraceptive intention, age at last live birth, education, and parity: United Statas, 1970-73

Contraceptive intention, age at last live birth, education, and parity

PREVENT UNWANTED PREGNANCY2

Age at last Iive birth /

15-19 years ..... ................ ...... ............... .................................................. ..................... ........

20-24 years ........... ........................................ ...... ................................ ................................

25-29 years .. .................................................. ............ .........................................................

30-34 years .. ...... ......................................................................................................... ........

35-39 years .. ..... .................................. .............................. ......... .......... ...............................

Education

Less than 12 years ................. ........................................................................ ........ .............

More than 12 years ................ ...... ........ ................ .. ...................................... ................ .......

Parity

No live births ....... .............. .. ................ ............ ................ .......................... .......... .... .. .........

One live birth ......................................................................... .......... .............. .. ........ ...... ....

Two live births ................ .......... ....................... ....................... ........ ...... .......................... ...

Tiiree live tirths ........ ...................... .............. .. ...... ................ .......... .............. .. ............ .......

Four live tirths ....... .. ...... .............. ................ .. ................ ...... ..............................................

Five live tirths ....................... .............................. .......................... .............................. .......

Six or more live births .......... ................................ ................ ...... ........ ................ ........ ...... ..

DELAY WANTED PREGNANCY

Age at last live birth

15-19 years ... ............. .............. .................. ............ .................. .............. ........ ................ .....

20-24 years ....... ........ ...... .......................... ...... ........................................................ ............

25-29 years ..... .. ........ ............ .. ................ .............. ........ .. ...... ..............................................

30-34 years ............................. ..... ........... ...................................... .. ............................ ........

Education

Less than 12 years ...................... ...... ...................................... ........................ .. ..................

12 years ................ ............ ........ .. ............ .. ...... .. ........ ...... .. ...... ........ ...................... ..............

More than 12yaars ... ............................. ..................................................................... ........

Parity

No live births .... .............. ....... ..... ...................... .......... ....... .............. .......... ............. ............

One live birth ...................... ............................................ .............................. .....................

Two live births ............... .... ...... .............................. .. ...................... ...... .. ........ ....................

Three live births ... .................... .. ...... ........ .............. ........ ................ .... ............................ .. ..

Relative age

Total ILow Low I

High High

middle middla

7.1

6.1

2.9

1.6

1.1

4.2

3.8

2.9

5.0

4,4

4.6

3.1

2.1

1.6

4.4

9.9

5.6

8.4

7.3

8,6

7.2

6.5

7.5

5.8

9.6

4.1

8.7

9.0

5.4

*

●

12.8

0.7

*

*

*

12.4

6.9

7.4

8.2

10.5

10.0

*

*

14.1

4.1

*

4.7

9.3

11.7

14.3

Percent

5.3

5.5

2.9

“*

*

3.8

4.8

5.5

*

6.2

6.7

2.2

3.9

6.6

8.4

6.2

18.8

*

6.3

8.8

7.4

12.6

3.6

10.1

*

5.4

2.6

2.4

*

1.2

4.3

3.1

4.7

9.3

3.8

2.8

10.9

14.5

4.8

7.6

*

5.9

7.6

7.0

4.7

8.0

0.5

*

4.7

3.1

1.4

1.1

0.7

2.7

2.2

6.6

0.2

2.2

3.0

1.5

2.8

*

6.6

7.1

5.4

9.5

8.1

5.5

3.4

7.4

9.7

*

lThe ~e~ult5 are b~~ed on ~ontra~eptiv~ USE. i~t~~~~ d~~ing which the woman was continuously married, but the woman need not

have been married during the entire 3-year period covered by the study.

21ncludes sterilization.

62

W.S. GOVERNMENT PRINTING OFFIWJ 1980 311-240/17 1-3
Series 1.

Series 2.

Series 3.

Series 4.

VITAL AND HEALTH STATISTICS Series

Programs and Collection Procedures. –Reports which describe the general programs of the Nat’onal

Center for Heafth Statistics and its offices and divisions and data co]lectjon methods used ~d i. ;Iude

definitions and other material necessary for understanding the data.

Data Evaluation and Methods Re~earc/t– Studies of new statistical methodology including experimental tests of new surwey methods, studies of vital statistics collection methods, new analytical

techniques, objective evaluations of reliability of collected data, and contributions to statistical theory.

Analytical Studies.--Reports presenting analytical or interpretive studies based on vital and health

statistics, carrying the analysis further than the expository types of reports in the other s,.rles.

Documents and Committee Refrorts--- Final reDorts of malor committees conccrnerf with vital and

heaJth statistics and documents’ such as recommended moc~el vital registration laws and revised birth

and death certificates.

Series 10. Data Fro m the Health Interview Survey. –Statistics on illness, accidental inJuries, disability, use of

.Teri(i 11

.!i(,ries I 2.

SeriPs 1 .?.

Series 14.

.$ffies 20.

Series 21.

hospital, medical, dental, and other services, and other health-related topics, all based on data collected

in a continuing national household interview survey.

i)uta brom the l{ealth Examination ●Survey and the Health and ,k’utrition Examination Surc,ey. –Llata

f’rom direct examination, testing, and measurement of national samples of the civilian noninstitu -

tionaliz.ed population provide the basis for two types of reports: (]) estimates of the medically defined

prcvafence of specific diseases in the LJnited States and the distributions of the population with respect

(C) physics], physiological, and psychological characteristics and (~) ~a]ysis of relationships among the

various measurements without reference to an explicit finite universe of persons.

Iluta b’ro m the Institutionalized Population Surveys. Discontil)l~cd effective 1975. Future reports from

these suneys will be in Series 13.

Data on Healtk A’e$ourcci [rti/ization..– Statistics on the utiiilation of health manpower and f.icilitics

providing long-term care, ambulatory care, hospital care, and fismily planning services,

Data on Health ReTouTccs: iManpower and Facilities. .- Statistics on the numbers, geographic dlstri

bution, and characteristic-s of health resources including ph,,si, Ians, dentists, nurses, other health

occupations, hospitals, nursing homes, and outpatient facilities.

Data on i%fortality. Various statistics on mortality other than ,i. included it] regular ,mnu~] or monthly

reports. Special analyses by cause of death, age, and other dem,,graphic va~-iat}les, ~eograpbic and time

sf’nm anaiys,cs; and statistics on charactrri5ti{ ,S ()[ deat}l~ nr,t avli]able fro,n t~,e vj~31 ~ec-or(]s [)a5ed ~)n

sample suneys of tllosr records,

r%to or Y;i!alir v. .\fa)7iage, c7z(1 [)i~~r~e. -Val-:ous ,:atistl,i :!!, natallty, marria~c-, an{] {iiv(>rce other

thao as l,~ciuded IrI rnglllar annual or montblv re}]orts, S})e( J1 analyses i)y demographic{ variables;

geographi( and time series analyses; studies of fertil!ty; ;md statistics [,1, characteristics of births not

available from the vital re(ords based on sample surveys of those Iecords.

Series 22. Data [’r:I r, fhe A’ati) )!. [ llor-f(~lity and ,Votulit) Sur7ey3. Dis( (JnTinuecl effcc tlve 19’75. h (lLure reports

from thrse s~mpie sIInrys I)ased on vital re(ords will be included }n Series 20 a~id 21, rrspcctjvelk

,Series 2.?. Data From the .Nation~l Surt:e ], 0 f 1’ami/y Crowth. StatLstI{ > on fertilit} famil~ formation and dissolution, famify planning, ~nd related maternal and inf~lt hedlth topics derived lr~, m a biennial survey

of a nationwide probability sample of ever-married women I s.44 years of age.

For a list of titles n! reports i)ut)llshed in these series, write to: S( irntific and ‘1’echnic,{i Intc)rm,l(lorl Branch

.Vaticrnd Center f(]r [fralth Stdtlstics

Publi[ IIcaltb Serw,ic(

!Iyattsrille, Afd. 2078?
NCHS

U S DEPARTMENT OF HEALTH AND HUMAN SERVICES POSTAGE AND FEES PAIO

Publ,c Health Se,v,ce

Of f,,, of Healfh Research, Stat,,,,.,, and Technology u S OEPARTMENTOF H H S

Natm.al Cmrw for Heallh StaI,sms

3702 East West H(ghw.ay HHS J9fj

Hyamv!lle, Maryland 20782

THIRD CLASS

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