NATIONAL CENTER Series 4 

For HEALTH STATISTICS INumber 1 

VITAL and HEALTH STATISTICS 

DOCUMENTS AND COMMITTEE REPORTS 

PROPERW OF THE 

PUBLICATIONSBRANCH

EDITORIALLIBRARY 

A Report of the United States National 

Committee on Vital and Health Statistics 

Recommendations concerning the collection and interpretation of data on fertility in the National Center for Health Statistics and the U.S. Bureau of the Census and discussion of 

the period and cohort measures of fertility, the interview survey as a source of fertility data, and the problems of projecting fertility rates. 

Washingtan, D .C. September 1965 

U.S. DEPARTMENT OF 

HEALTH, EDUCATION, AND WELFARE Public Health Service 

Anthony J. Celebrezze Luther L. Terry 

Secretary Surgeon General 
I’uhlic Hefilth Ser\,ice Publication No. 1000-Series 4-No. 1 

For sale by the Superintendent of Documents, U.S. Government Printing iXfice 

‘Washington, D.C., 20402 - Price 25 cents 
NATIONAL CENTER FOR HEALTH STATISTICS 

FORREST E. LINDER, PH. D., ~&C~O?’


“rHEODORE D. WOOLSEY, &j@y Director


O. K. SAGEN, PH. D., ~$~iftanf Dirwtor


WALT R. SIM.MONS, MA., Stathicul Advisor


ALICE M. WATERHOUSE, M. D., Medical Advisor


JA.MES E. KELLY, D. D. S., Dental Advi~or


LOUIS R. STOLCIS, MA., Executive Oficer


OFFICE OF HEALTH STATISTICS ANALYSIS 

IWAO M. MORIYAMA, PH. D., Chief 

DIVISION OF VITAL STATISTICS 

ROBERT D. GROVE, PH. D., CItiej 

DIVISION OF HEALTH INTERVIEW STATISTICS 

PHILIPS. LAWRENCE, Sc. D., Chief 

DIVISION OF HEALTH RECORDS STATISTICS 

MONROE G. SXRKEN,PH. D., Chief 

DIVISION OF HEALTH EXAMINATION STATISTICS 

ARTHURJ. MCDOWELL, Chief 

DIVISION OF DATA PROCESSING 

SIDNEY BINDER, Chief 

Public Health Service Publication No. 1000-Series 4-No. 1 

Library of Congress Catalog Card Number 6-5-62149 
This report, prepared under the auspices of 

the U.S. National Committee on Vital and Health 

Statistics, is concerned with the adequacy of 

measures currently available to indicate change 

in fertility trends. It discusses the problems of 

fertility measurement and recommends other 

sources of data for assessment of trends and for 

projections of fertility rates. Also, recommendations are made for research and development 

needed in the field of fertility statistics. 

It is hoped that this report will serve as a 

basis for further discussion by organizations and 

agencies capable of providing needed data and 

that it will stimulate research and special studies. 

Robert Dyar, M.D. 

Chairman 

... 

Ill 
THE UNITED STATES NATIONAL COMMITTEE ON VITAL AND HEALTH STATISTICS 

Robert Dyar, M. D., Chairman Everett S. Lee, Ph.D.


Chief, Division of Research Associate Professor of Sociology


California State Department of Public Health University of Pennsylvania


Berkeley, California Philadelphia, Pa.


I. M. Moriyama, Ph. D., Secretary


Chief, Office of Health Statistics Analysis


National Center for Health Statistics


Public Health Service


U.S. Department of Health, Education, and


Welfare 

Washington, D.C. 

Loren E. Chancellor, Director


Division of Vital Statistics


State Department of Health


Des Moines, Iowa


William M. Haenszel


Biometry Branch


National Cancer Institute


National Institutes of Health


Bethesda, Md.


Dudley Kirk, Ph. D., Demographic Director


The Population Council


New York, N.Y.


THE SUBCOMMITTEE 

Clyde V. Kiser, Ph. D., Chairman


Senior Member, Technical Staff


Milbank Memorial Fund


New York 5, New York


Anders S. Lunde, Ph. D., Secretary


Assistant Chief, Division of Vital Statistics


National Center for Health Statistics


Public Health Service 

U.S. Department of Health, Education, and 

Welfare 

Washington, D.C. 

I. M. Moriyama, Ph. D., Ex-Officio


Secretary, U.S. National Committee on Vital and


Health Statistics 

Washington, D.C. 

Donald S. Akers


Population Division


U.S. Bureau of the Census


Washington, D.C.


aForrnerly Scripps Foundation for Research in Population 

Problems. 

Iv 

Forrest E. Linder, Ph. D., Director


National Center for Health Statistics


Public Healti Service


U.S. Department of Health, Education, and


Welfare


Washington, D.C.


Walter J. McNerney, President


Blue Cross Association


Chicago, 111.


Conrad Taeuber, Ph. D., Assistant Director


U.S. Bureau of the Census


U.S. Department of Commerce


Washington, D.C.


Jacob Yerushalmy, Ph.D.


Professor of Biostatistics


School of Public Health


University of California


Berkeley, California


Franklin D. Yoder, M.D.


Director of Public Health


State of Illinois Department of Health


Springfield, Ill.


ON FERTILITY MEASUREMENT 

Arthur A. Campbella


Chief, Natality Statistics Branch


Division of Vital Statistics


National Center for Health Statistics


Public Health Service


U.S. Department of Health, Education, and


Welfare


Washington, D.C.


David Goldberg, Ph. D.


Department of Sociology


University of Michigan


Ann Arbor, Michigan


Wilson H. Grabill


Chief, Family and Fertility Statistics Branch


Population Division


U.S. Bureau of the Census


Washington, D.C.


Norman B. Ryder, Ph. D.


Department of Sociology


University of Wisconsin


Madison, Wisconsin

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CONTENTS


Page 

Foreword 

Introduction 

General 

Objectives 

Conclusions and Recommendations 

I. A Change in Fertility.Has Been Developing in the United States 

II.	 Currently Published Measures Are Adequate to Refle<t Certain 

Changes in Fertility but Require Improvement and Refinement 

III. More Research is Required in the Area of Fertility Projections 

IV.	 Further Research is Required in Areas Where Data Are Absentor 

Scarce 

V.	 Information on Fertility Developments Should be Communicated to 

the Public 

Chapter I. Fertility Statistics From the National Center for Health StatisticsTypes of Data Published 

Recent Trends in Fertilityas Determined From Natality Statisti~s 

Future Publication Program 

Chapter II. Census Data in fertility 

Types of Data Collected 

Recent Trends in Fertility According to Census Data -------------------

Prospects for Future Data -------------------------------------------

Chapter III. Period Fertility and Cohort Fertility: Their Measurement and 

Interrelation 

Chapter IV. Evidence of Change in Current Fertility 

Changes in Cohort FertiliW 

Changes in Period Fertility 

The Relationship Between Fertility Trends and Economic Conditions 

Chapter V. The Survey as aSource of Fertility Data ---------------------

Chapter VI. Fertility Changes-Implications for Population Projections 

Activity in the Field of Projections 

Problems in Methodology 

References 

Appendix. Dfinitions of Terms 

Fertility Concepts 

Fertility Measures 

1. Measures of Period Fertility 

2. Measures of Cohort Fertility 

... 111


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IN THIS REPOR T theprestmt means of measuring feytility in the United 

States aye pvesented and discussed in teyms of the adequacy with which 

they poytyay cwwent tyends. 

Data published by the National Center fov Health Statistics such as the 

cwde bivth rate, age-sex-adjusted birth rate, gross Reproduction ~ate, 

and geneyal fertility rate indicate recent declines in fentility. Plans foy 

the development of new measuyes include additional cohoytfeytility Yates, 

followback studies, and the use of pyoposed new iteww of information on 

the Yevised U.S. Standard Certificate of Live Birth. 

Data pyepayed by the U.S. Bureau of the Census include data on women 

by numbey of childyen evey born, on women by number of children pYesent in the home, ad on childspaci~. Plans foy the future include obtaining additional data from the Cuwent Population Survey. 

The inteyyelationship of peyiod and cohoyt measuyes is descyibed, and 

the evidence of change in cuwent feytility, as demonstrated by these 

measuyes, is analyzed. 

FeYtility intemiew suweys mea.swe aspects of fertility not available 

from bivth YegistYation OY the decennial census. Bivth expectations data 

are an impoytant adjunct to the analysis of cwrent trends. 

Population projections have not taken account of all the vayiables which 

have a beaying on feytility. The introduction of social and economic as 

well as demographic variables is necessary for the improvement of projection methodology. 

It was concluded that a change in feytility has taken place in the United 

States, that cwwentlypublished measuyes aye adequate, that these measuyes can be impyoved and should be supplemented by smweys, and that 

fwthey Yeseavch should be encounzged in the field of feytility measurement. Recommendations diyected toward the improvement of the measures and suggestions for the extension ofvesearch are pvovided. 

SYMBOLS 

I Data not available I 

I Category not applicable . . . I 

Quantity zero -

Quantity more than O but less than 0.05 ----- 0.0 

Figure does not meet standards of 

* reliability or precision 
FERTILITY MEASUREMENT


REPORT OF THE U.S. NATIONAL COMMITTEE ON 

VITAL AND HEALTH STATISTICS 

INTRODUCTION 

General 

A new wave of interest in fertility trends in 

the United States has been created by such diverse 

situations as the current decline in the crude birth 

rate, the open discussion of fertility regulations, 

the impending increase of youngsters entering the 

labor market, marrying, and starting families of 

their own, and the rapid expansion of the world 

population. 

A postwar peak in the number of births was 

reached in 1957, when about 4.3 million live births 

were recorded. The crude birth rate for that year 

was 25.3 live births per 1,000 population. Since 

1957 the annual number of live births has hovered 

around 4.2 million, and the crude birth rate has 

declined every year. The rate for 1964 was about 

21.2, the lowest since 1945. The general fertility 

rate declined from 122.9 births per 1,000 women 

of childbearing age (15-44 years) in 1957 to 105.6 

in 1964 (see figure 1). 

That a downturn in the Nation’s fertility had 

taken place became ap~arent by”the latter half of 

1961 after the seasonally adjusted birth rate and 

fertility rate had declined for several months. The 

decline continued almost without interruption 

through 1964. By the end of 1964 the birth rate and 

the fertility rate, seasonally adjusted, were about 

13 percent below the rates 4 years earlier. More 

refined measures of fertility such as the ageparity-specific fertility rates have revealed that 

women of almost all ages and parities have contributed to the current decline in fertility. 

Questions have been raised concerning the 

significance of the decline. Was it to be of short 

duration? Was it a return to the long-range decline apparent before World War I? Questions 

also have been raised concerning related developments such as the apparent decline in age-specific 

fertility, the shift from the temporary shrinking 

of the group of women of childbearing age to the 

impending entrance of the baby boom youngsters 

into the labor force, and reproductive ages. There 

also have been questions abut the achievement 

of desired family size by the major childbearing 

cohorts. On another level questions have been 

raised regarding the effect of motivations, expectations, desired family size, and socioeconomic factors on fertility change. 

This increased interest has raised questions 

concerning the adequacy of measures of fertility 

in current use, the problem of developing better 

measures of fertility, and the means by which the 

findings of fertility research may be better communicated. In the hope that it would contribute to 

a better understanding of these questions, the 

U.S. National Committee on Vital and Health Statistics in 1963 named a Subcommittee on Fertility 

Measurement to study these matters and to prepare a report. The importance of fertility meas-
MILLIONS BIRTHS PER 1,000 

OF BIRTHS WOMEN AGEO 15-44 

[Trend lines for 1959-65 based on reglsfercd live births; trend lines for 1910-59 based c+ live births adjusted for underrngistrotlonl 

5 200 

4 

3 .S . . . ..+.9 . . . . 

* 

2 

I 40 

0, 111111111 111111111 111111111 111111111 111111111 111111111 0 

1910 1920 1930 1940 1950 1960 1970 

Figure 1. Live births and fertility rates, 1910-64. 

urement has been emphasized in tl-e reports of 

three previous subcommittees infertility: 

(1) Statistics needed concerning fertility, 

Vital Statistics—Special Reports, Vol. 

33, No. 11, Feb. 25, 1952. 

(2)	 trogress in development of fertility statistics and population estimates, Vital 

Statistics—Special Reports, Vol. 39, No. 

8, May 14, 1956. 

(3)	 Fertility studies based on data for the 

1960 census period, Vital Statistics— 

Special Repovts, Vol. 47, N0. 5, June 8, 

1959. 

Objectives 

The objectives of this study were 

General: To determine whether a change in 

fertility is developing and whether currently published measures are adequate to reflect changes 

in fertility; to recommend needed improvement 

or alternative series with aviewto providing the 

best feasible measures of current trends offertility in the United States; to give attention to 

measures that might have some value for projections into the future; and to recommend research that may be needed in order to develop 

such measures. 

Specific: To report, in particular, on the 

followinx 

(1) 

(2) 

(3) 

(4)


(5) 

(6) 

(7) 

Period fertility and cohort fertility: their 

measurement and interrelation. 

Evidence of change in current fertility 

(period and cohort). 

Fertility statistics in the National Center 

for Health Statistics. 

Census data on fertility. 

Population projections. 

The use of sample surveys in fertility 

research. 

Recommendations. 

2

CONCLUSIONS AND 

RECOMMENDATIONS 

The following are conclusions from this 

study with appropriate recommendations: 

1. A Change in Fertility Has Been 

Developing in the United Statesb 

There is no doubt about the decline in period 

fertility rates during the past several years. All 

the currently published measures portray this 

decline. 

The high birth rates foIlowing World War II 

had been associated with earlier age at marriage, 

early family formation, and an increase in the 

average size of the family. The change iit fertility 

after 1957 was due partly to changes in the age 

composition of the population: in 1960 there were 

over 1 million fewer women in the most fertile 

age group (20-29 years) than in 1950. The decline 

in the birthrate was due also to lower age-specific 

rates after 1957. It seems probable that during 

the remainder of this decade the age-specific 

birth rates above age 30 years will continue to 

decline and that rates beIow age 30 may decline 

or stabilize at their current levels. The trend toward earlier marriages has ceased: For reporting 

Stat~s the median age of brides at first marriage 

leveled off at 19.9 years after 1958, and the median 

age of grooms at first marriage leveled off at 

23 years, or slightly under, after 1959. 

The trend toward younger childbearing may 

have reached a limit; the median age of mothers 

at the birth of the first child is still low but has 

leveled off since 1960 at 21.4 years. 

bf)~’~initian of fertility. For many years in the United States 

the gonernl term fertility has been take: ,to refer to tbe actual 

numborofchildren born within a given trme period, by a given 

age, or during a lifetime. As such it is distinguished from fecundity, which related to the physiologiccal capacity @ reproduce. The fertility or the reproductive performance of an aggreguto of individuals may be expressed as a rate or as rates, 

each rate having a numerator of live births occurring to a specifia population in a specified time period and a denominator 

of a number of persons, women, or person-years of exposure 

with tbe same specifications. In this sense fertility is the’ 

rata at whioh children are born in a given population within a 

given time period or to a cohort of women by a given age or 

oyer a lifetime. 

Cohort fertility data indicated that the trend 

toward higher completed fertility may be approaching an upper limit. 

Data on expectations of women on the number 

of children they expect to have in the next few 

years show that more recent cohorts (those of 

1936-42) expect fewer chihiren than those of 1931-

35. It now appears likely that complete fertility 

will stabilize or decline slightly among cohorts 

lmrn in the late 1930’s and early 1940’s. 

Because of the complexity of the problem it 

is not possible to suggest specific types of data 

that will give definitive answers to questions 

regarding future trends in period or cohort 

fertility. Major political, economic, and social 

changes could bring unpredictable changes in 

marriage rates, birth rates, and family size. 

In regard to the immediate future, increased 

numbers of potential parents are beginning to 

enter the picture as a result of the large contingents of babies born following World War II. 

The rates at which these groups will marry and 

raise families are not known. Period measures 

provide only slight clues about future trends. The 

main indication of future developments in cohort 

fertility is that afforded by data on expectations 

regarding number of children. 

Il. Currently Published Measures Are 

Adequate to Reflect Certain Changes 

in Fertility but Require Improvement 

and Refinement 

Currently published national birth rates indicate the existence of changes in period fertility. 

A deficiency in these data, and one which makes 

interpretation difficult, is the lack of information 

on the marital characteristics of the population. 

Data such as age at marriage and duration of 

marriage for the parents and for the total childbearing population in each year are necessary to 

obtain a more complete picture of the factors 

underlying the changing birth rates. In addition, 

information on the spacing of children in relation 

to date of marriage and date of birth of the 

previous child would permit an evaluation of the 

effects of changes in the timing of births in terms 

of both period and cohort fertility measures. In3 
formation on socioeconomic status of parents 

would also be useful. 

It is recommended that the National Center 

for Health Statistics request more information on 

the Standard Certificate of Live Births. A question 

on month and year of previous birth and also month 

and year of first marriage should be added. An 

item on education of mother and father on the 

certificate would lay the foundation for better 

statistics on socioeconomic differentials in fertility. 

The National Center for Health Statistics 

should press more vigorously toward improvement of the data on marriage and divorce, 

since both of these are highly relevant to fertility trends. The marriage-registration area, 

which now includes 36 States, and the divorceregistration area, comprised of 22 States, should 

be expanded to include all States as quickly as 

possible. While it is recognized that many problems exist, the National Center for” Health Statistics should work closely with the States to 

bring this about. The Center is to be commended 

for its development of the marriage-registration 

area and the divorce-registration area through 

the present time. 

It is recommended that the National Center 

for Health Statistics through its Vai-ious Divisions 

contribute to the development of new data in the 

area of fertility statistics. This may be done 

through followback studies and by questions on 

the number of children ever born and the date 

of first marriage of married women in the 

National Health Survey. The Center could gradually build up a store of data that would permit 

analysis of nuptiality and fertility in relation to 

health and disease. 

As for cohort fertility, currently published, 

national data provide only a background for 

changes in fertility in t&ms of past cohort behavior. Special studies involving an interweaving 

of cohort fertility data and data on fertility expectation for younger women would help provide 

clues regarding trends in cohort fertility. 

It is recommended that two series of cohort 

fertility rates be maintained, i.e., one for birth 

cohorts and one for marriage cohorts. Birth 

cohort fertility is influenced both by marriage 

rates and marital fertility. Marriage cohort 

fertility indicates the fertility trend for married 

women by duration of marriage. 

The U.S. Bureau of the Census is to be 

commended for its continuous efforts to collect 

detailed and meaningful data on fertility. The 

Subcommittee endorses the periodic collection 

of information on children-ever-born and childspacing. 

In some cases the Bureau has collected and 

tabulated important data that cannot be published 

because of insufficient funds. In such instances 

efforts should be made to obtain money from other 

government agencies or private organizations to 

publish the data. 

Ill. More Research is Required in the Area 

of Fertility Projections 

R m axiomatic among demographers that 

fertility is extremely difficult to predict. Human 

reproduction is especially sensitive to unforeseen 

changes in the social, political, and economic life. 

Nevertheless, the importance of such projections 

in the national life and at local levels should be 

recognized. It is recommended that the Bureau 

of the Census and the National Center for Health 

Statistics increase their investigations in this 

area. 

Through the Current Population Survey the 

Bureau of the Census should collect periodic 

data on expectations regarding ultimate size of 

family and expectations of births during the next 

5 years. Research on models for population projections is wholeheartedly endorsed. The National 

Center for Health Statistics should itself enter the 

field of making fertility projections. 

It is also recommended that the work of private institutions be sustained and enlarged. Research of the type being done in the Growth of 

American Families Studies, the Princeton Study 

of Fertility, and the Detroit Area Studies has already gone far in developing the techniques for 

collecting and analyzing expectations data, The 

periodic provision of data from the Current Population Survey and the Natality followback studies 

of the National Center for Health Statistics would 

provide national benchmark materials that would 

enhance the value of the work of private institutions 

collecting such data regularly. 

4 
IV. Further Research is Required in Areas 

Where Data Are Absent or Scarce 

Little is known about human fertility, which 

lies at the base of rapid population expansion, one 

of the pressing problems of our time. It is urgently 

required that research in human fertility be extended. 

It is recommended that foundations, universities, and other private institutions in the United 

States continue their efforts in areas in which 

official data are absent or scarce. This includes, 

in particular, data on family planning practices 

and attitudes, fecundity and fecundity impairments, and religion of parents. Because of the 

persistence of high fertility among nonwhites and 

Catholics in the United States, studies especially 

designed for these groups should be encouraged. 

V, Information on Fertility Developments 

Should be Communicated to the Public 

While there is considerable public interest 

in the subject of population growth, there appears 

to be a need for the education of the general public 

in the meaning of birth statistics. In addition to 

supplying technical information to other agencies 

of the National Government and to the vast number 

of economic and other organizations which utilize 

the data, the Bureau of the Census and the National 

Center for Health Statistics are urged to devote a 

portion of their program to those publications 

which will inform the lay public concerning their 

work. 

It is recommended that the National Center 

for Health Statistics continue to prepare periodic 

evaluations of current fertility trends that would 

bring together all of the latest information on 

cohort fertility, timing, and expected childbearing 

from a variety of sources. Particular attention 

should be given to estimating the extent to which 

recent variations result from” changes in the 

timing of fertility as compared with changes in the 

size of completed family. This review of current 

trends should be written in nontechnical language 

and be made available to the news media. It may 

include a technical discussion for demographers, 

but its main purpose should be to give to laymen 

a well-informed discussion of the meaning of current birth statistics. 

CHAPTER 1. FERTILITY STATISTICS 

FROM THE NATIONAL CENTER FOR 

HEALTH STATISTICS 

Types of Data Pulished 

The Division of Vital Statistics, National 

Center for Health Statistics, is responsible for 

producing the Nation’s basic source of fertility 

statistics, published in the annual Natality volume 

of Vital Statistics of the United States. The volume 

contains detailed frequency tabulations of births 

for each State, each metropolitan area, and other 

geographic areas. Data are shown by color, sex, 

nativity of white mother, month of birth, age of 

father and mother, birth order, attendant at birth, 

birth weight, plurality, and legitimacy. Each 

volume also contains period and cohort fertility 

rates. The period fertility rates include the crude 

birth rate, age-sex-adjusted birth rate, general 

fertility rate, age-specific birth rate, gross reproduction rate, net reproduction rate, birth rate 

by age of mother and live-birth order, birth rate 

by month, illegitimacy rate and ratio, and intrinsic 

rate of birth, death, and natural increase. The 

data based on cohort fertility analysis include ageparity-specific rates and percentage distributions 

of the female population by age and parity. Prior 

to 1962 the Natality statistics volumes include a 

brief analysis of birth statistics focusing on the 

current year. Included as new measures of fertility are cumulative birth rates for cohorts of 

women and the total fertility rate. These will be 

incorporated as a regular feature into subsequent 

volumes of Vital Statistics of the United States. 

In addition, the Division publishes the 

Monthly Vital Statistics Repovt (MVSR), which 

presents provisional statistics on births by month 

as reported by the States and provides crude birth 

rates and general fertility rates for the month. 

An advance report of final natality statistics for 

the year appears annually in the MVSR prior to 

their publication in Vital Statistics of the United 

States some months later. The advance report 

includes a brief analysis of the Nation’s fertility 

for the year supplemented with tables showing 

fertility rates by age of mother, live-birth order, 

and color. 

5 
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Provisional fertility data on a monthly basis 

are also published in the Health, Education, and 

Welfare Indicators; these include a time series 

of birth rates and fertility rates, adjusted and 

unadjusted for seasonal variation, and a brief 

descriptive statement of the trend of these period 

measures. 

Separate publications include the former 

Vital Statistics—Special Reports, which have 

from time to time provided details on births by 

age of mother, color, and live-birth order; childspacing; cohort fertility; quality of birth statistics; 

illegitimacy rates and ratios; and other selected 

topics that are now reported in Series 21 of the 

National Center for Health Statistics Report 

Series. AH the natality tabulations are derived 

from information on the certificate of live birth 

as provided by each State. The nature and scope 

of the fertility measures are therefore limited 

by the content of the certificate. The Standard 

Certificate of Live Birth is prepared by the 

National Center for Health Statistics in close 

collaboration with representatives of the various 

States and is revised about once every 10 years. 

A revision of the present certificate is now under 

consideration and is expected to be recommended 

to the States for adoption as of January 1, 1967. 

The items proposed for revision reflect both the 

continuing interest in an improved document as a 

.— 

statistical source and the present need for new 

and refined fertility measures. 

Recent Trends in Fertility as Determined 

From Nataiity ~Statistics 

A decline in actuaI numbers of births in the 

United States has been evident since 1957, when the 

largest annual number of births was recorded 

(4,308,000). In 1963 the number of births was 

4,098,020, which is 4.9 percent below that in 1957. 

The decline was experienced by Mb white and 

nonwhite groups, as indicated in table A, 

All the conventional measures of fertility 

also showed declines during this period: 

Percent 

1963 1957 change 

Crude birth rate (per 

1,000 popuIation)---- 21.7 25.3 -14.2 

Age-sex-adjusted birth 

rate (per 1,000 population) 28.4 32.2 -11.8 

Gross reproduction 

rate 1,623 .01,837.0 -11.6 

General fertility rate 

(per 1,000 females 

15-44 years 108.4 122.9 -11.8 

Table A, Live births by color: United States, 1957-63 

Year 

19631 . . . 

;;:;1 . . . . 1960 

1959 

19582 . . --”------

19572 

Total 

4,098,020 

4,167,362 

4,268,326 

4,257,850 

4,244,796 

4,255,000 

4,308,000 

Number of births 

White I Nonwhite 

3,326,344 ‘ 638,928 

3,394,068 641,580 

3.600.864 667,462 

;;;:;;;:: 657; 106 

647,366 

3;598:000 657,000 

3,648,000 660,000 

lFi~res by color exclude data for residents of New Jersey because this State did 

not re~uire rkporting of the item. 

zBirths adjusted for underregistration. 

Source: National Center for Health Statistics: Vital Statistics of the United Statesl 

1963, Volume 1. Public Health Service. Washington. U,S. Government Printing Office, 

1964. sec. 1, table 1-2. 

6 
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The crude birth rate, which is the most 

widely used measure of fertility, showed the 

greatest decline during this period. The crude 

birth rate, however, is not an adequate measure 

of fertility because its comparability over a period 

of years maybe affected by changes that take place 

in the age and sex composition of the population. 

By standardizing this rate to the 1940 population 

of the United States, a figure free from this kind 

of distortion can be derived. The standardized, or 

age-sex-adjusted, birth rate decreased about 12 

percent during the period 1957-63. 

The general fertility rate, which measures 

births in terms of the population at risk—women 

in the childbearing ages—also showed a decline 

of almost 12 percent, from 122.9 to 108.4 live 

births per 1,000 females aged 15 to 44years. The 

general fertility rate, while it is more refined than 

the crude birth rate, can still be affected by differences in age composition among females within 

the childbearing period when comparisons are 

made over several years, By looking at the fertility of females in 5- year age groups, this problem 

of comparability is largely overcome. The agespecific rates shown in table B reveal that women 

of every childbearing age experienced a declining 

rate of childbearing during the period 1957-63. 

The gross and net reproduction rates, essentially summary measures of this array of 

rates for all eight age groups, showed declines 

of over 11 percent during the period. 

One of the most specific measures of fertility now available is the age-parity-specific 

birth probability. It is the probability that a 

woman of a given parity and exact age x will bear 

a child before reaching exact age x+1. Summaries 

of such probabilities for 5-year age groups are 

presented for recent years in table C. They show 

that in the main childbearing ages women of nearly 

all parities have contributed to the recent decline 

in fertility. 

The rates now published indicate adequately 

the main trends in period fertility in the United 

States. However, the Division recognizes the 

desirability of publishing additional measures to 

aid in understanding the factors underlying these 

trends. To obtain such measures, it would be 

necessary to have better information than is now 

available on such topics as the marital status of 

parents and their duration of marriage. An important step toward this goal would be to obtain 

the date of first marriage. This would permit 

comparisons of the family building patterns of 

women marrying indifferent years and at different 

ages. Better legitimacy and illegitimacy rates 

could be prepared. Although the proportion of 

births that are illegitimate is small (about 6 percent in 1963), trends in the rates for these births 

Table B. Birth rates by age of mother: United States, 1957-63 

Age of mother 

Year 10-14 15-19 40-44 45-49 

years years years years 

=E=El== 

1963 ------------------------- 0.9 76.5 231.3 185.4 105.9 51.2 14.2 0.9 

1962 ------------------------- 0.8 81.3 243.8 191.3 108.7 52.6 14.8 0.9 

1961 ------------------------- 0.9 88.0 253.6 197.8 113.3 55.6 15.6 0.9 

:;;;---”-” 0.8 89.1 258.1 197.4 112.7 56.2 15.5 0.9 

k-- ”----- 0.9 89.1 257.5 198.6 n:,; 57:3 15.3 0.9 

260,6 1 I 

58.3 15.7 

1 

;;;;: -”---------” 0,9 91.4 258.2 198.3 0.9

---P--.- # 1.0 96.3 1199.4 118:9 59.9 T16.3 1,1

1Births adjusted for underregistrat ion. 

Source: National Center for Health Statistics: Vital Statistics of the United States, 

1963, Volume I. Public Health Service. Washington. U.,S. Government Printing ff~ce, 

1964. sec. 1, table 1-6. 

7

Table C. Birth probabilities for specified years, by exact age and parity of mother: 

United States, 1957, 1960, and 1963 

Exact age of mother as of 

January 1 each year 

20-24 years 

1963---------------------

1960---------------------

1957---------------------

25-29 years 

1963---------------------

1960---------------------

1957---------------------

Parity 

o 1 2 3 4 5 

163.7 312.2 252.8 260.4 300.0 351.8 

186.8 341.4 281.0 299.8 349.7 406.0 

194.7 337.8 275.8 295.5 348.4 414.4 

137.7 233.9 168.5 168.4 190.1 229.6 

140.2 252.3’ 181.0 183.7 207.6 258.3 

139 � 2 253.8 178.8 184.0 217.5 266.8 

Source: National Center for Health Statisti,cs:Vi,tal Statisticsof the United States, 

1963, Volume I. Public Health Service. Washington. U.S. Government Printing Offi,ce, 

1964. sec. 1, table 1-15. 

have some influence on the trend intotal fertility. 

This influence should be taken into accountin any 

complete analysis of fertility trends in this 

country.c 

Information required in relation to the timing 

of births would ideally include the dates of birth 

of each child born alive and eachfetaldeath. Date 

of the termination of last pregnancy andoutcome, 

while somewhat more limited, can also provide 

excellent material for studying current childspacing patterns. The addition of the latter 

question and an item of date of first marriage 

is being recommended on the next revision of the 

Standard Certificate of Live Birth. 

C$’tatistics on Wegitirnacy. The extent of illegitimacy is 

hard to measure. Illegitimacy ratios are derived by relating 

recorded illegitimate live births to total live births. Illegitimacy rates measure the number of illegitimate births per 1,000 

unmarried” women aged 15-44 years. The estimate of unmarried women is prepared by the Bureau of the Census on the 

basis of a sample survefi therefore, a sampling variability is 

associated with these rates. However,improvement in the 

measure of illegitimacy lies in another direction, the completeness of the record on illegitimate bl rths. Sixteen States do 

not require reporting on illegitimacy; there are misstatements 

on the birth record to conceal illegitimacy status. The most 

that can be said about the illegitimacy figures is that they indicate the minimum extent of illegitimacy. 

In order to broaden the interpretation of 

changes in fertility, further information is required on the socioeconomic background of the 

parents. The only useful item on the present 

Standard Certificate of Live Birth which has 

bearing on this matter is that ofrace or color. 

An item on occupation is not tabulated in the 

national statistics because ofreportingandcoding 

difficulties. An itemon education of the mother, 

particularly, would provide needed information, 

and this item is being considered for inclusionon 

the Standard Certificate. Details on family income 

and religion would be most useful, but it is improbable that these items will soon appear on 

the Standard Certificate. In the case of income 

and religion and other useful details which are 

not likelyto be placed ontheStandardCertificate, 

it is suggested that such information be obtained 

through surveys as is currently being done in 

fertility research. 

Future publication Program 

The program for natality statistics in the 

Division of Vital Statistics as regards tabulation 

and publications reflects the continuing developmerit of the National Center for Health Statistics, 

which underwent reorganizationin October 1963. 

8 
There is an increase in emphasis on the technical 

and professional aspects of the work. There has 

been a general speeding up of the publications 

timetable. The entire processing and publications 

schedule from the close of a data year to final 

publication is being reduced from about 24 months 

to approximately 12 to 14 months. As a consequence of the accelerated program annual Natality 

volumes for both 1961 and 1962 were prepared 

for publication during 1963. One factor in the 

speedup was the decision to exclude the textual 

analysis from the 1962 volume; the text was 

published separately in the new NCHS Report 

Series for Vital and Health Statistics, Series 21, 

Natality. This series will replace the vital 

Statistics—Special Repovts mentioned above. 

The 1964 annual Natality volume, which will 

also be prepared at an early date, will include a 

number of other changes and additions. Because 

of considerable interest in Negro fertility the 

category of nonwhite will include the subclass of 

Negro in major fertility tables (live births by age 

of mother and live-birth order for each State, 

metropolitan and nonmetropolitan counties in each 

State, and each standard metropolitan statistical 

area). Also, for the United States it is planned to 

tabulate live births by age of mother and livebirth order for specified races (white, Negro, 

Indian, Chinese, Japanese, and other races). The 

last detailed tables on multiple births were published in the 1958 annual volume. Since that year 

tables on live births in plural deliveries only have 

been published with no detail concerning those 

Imrn alive or dead in sets, by sex. It is plamed to 

collect and tabulate matched sets of multiple births 

beginning with data year 1964, contingent upon 

State participation. 

A special project on the fertility of Puerto 

Rico will be completed in 1965 by the National 

Center for Health Statistics. The introduction of 

new items on the Puerto Rican certificate of live 

birth has made possible studies on fertility by 

duration of marriage (legal and consensual unions) 

and by education of mother and father. 

In 1964 the National Center for Health Statistics took over the production of cohort fertility 

tables heretofore prepared by the Scripps Foundation for Research in Population Problems. It 

is anticipated that the methodology will be reviewed by the Bureau of the Census and the Division of Vital Statistics and possibly revised. In 

1960 the first of a series of special reports 

(Vital Statistics–Special Reports, Vol. 51, No. 1) 

“Fertility Tables for Birth Cohorts of American 

Women,” prepared by Whelpton and Campbell, was 

published. Additional cohort fertility rates will be 

published. 

A series of followback studies was started 

using the live-birth certificate as a sampling 

frame to provide more detailed information on 

many factors not otherwise available from the 

certificate. Annual sample surveys will be conducted to obtain information on childspacing, 

socioeconomic and health characteristics of parents, prenatal care, and birth expectations. 

Considerable attention has been given recently to the problem of data quality control. In 

addition, the National Center for Health Statistics 

is currently expanding its program of fertility 

research while continuing to provide basic natality 

data of general consumer interest. 

CHAPTER II. CENSUS DATA 

ON FERTILITY 

Types of Data Collected 

The Bureau of the Census obtains several 

types of data on fertility that complement birthregistration data. The data are collected in 

decennial censuses and in some monthly sample 

surveys of the population, the latter generally at 

2- or 3-year intervals. The main types of information collected are data on women by number 

of children ever born, data on women by number 

of young children present in the home, and occasionally data on childspacing or on intervals 

between births. Tables on the population by age 

and sex may also be used for some information 

on fertility, such as for ratios of young children 

to women of childbearing age, and, with the aid 

of certain adjustments, for the computation of 

other measures, such as gross and net reproduction rates by an indirect standardization procedure. The Bureau also provides the population 

bases used for the computation of birth rates 

from vital statistics and provides other data of 

9 
------------------

------------------

------------------

------------------

------------------

------------------

indirect value for the study of fertility, such as 

amual data on the marital status of the population 

and on household and family composition. Much 

of the data are available by geographic, demographic, social, and economic characteristics. 

Recent Trends in Fertility According to 

Census Data 

In general, decennial census data and current population survey data show that the average 

number of children ever born per woman at ages 

25 years and over is still increasing. There is 

some evidence that the trend toward earlier 

marriage and earlier childbearing has ceased for 

women under 25 years, but these young women 

have not completed a sufficient proportion of 

their lifetime childbearing for a valid assessment 

of their eventual family size. The figures in 

table D illustrate these points. 

It may seem from table D that the women 

aged 30-34 years in 1962 had already borne 

nearly as many children, on the average, as those 

35-39 years of age. The younger cohort probably 

had completed somewhat more than 75 percent 

of its eventual lifetime childbearing; and the latter, 

somewhat more than 93 percent. (The percentages 

cited are based on retrospective data for women 

44 years of age in 1959 obtained from fertility 

histories; because of their earlier marriage and 

childbearing the younger cohorts probably had 

completed more of their lifetime childbearing 

by ages 30-34 years or 35-39 years than the 

cohort that was 44 years of age in 1959. Data for 

1962 on the fertility expectations of married 

women, obtained by the Growth of American 

Families Study [not by the Census Bureau], indicate that women aged 30-34 years had already 

had 88 percent of their total fertility and those 

35-39 years of age already had 95 percent.) Even 

a large drop in birth rates at each remaining 

childbearing age for the cohort 30-34 years in 

1962 as compared with the cohort 35-39 years 

would result in considerably more children per 

woman by age 44 years for the younger cohort 

than for the older cohort. ‘This pattern of expected 

future increase in family size despite possible 

declines in annual birth rates at each advanced 

childbearing age may serve as a caution that 

secular trends in age-specific birth rates do not 

necessarily reflect correct trends in lifetime 

numbers of children per woman. 

Census data show that between 1950 and 1960 

the proportion of childless women and of women 

with only one child declined considerably, while 

the proportion with two or more children increased. For example, in 1960 among women 

aged 30-34 years who had ever married, only 

10.4 percent were childless, 14.7 percent had 

borne only one child, 62.4 percent had borne two 

to four children, and 12.5 percent had five or 

more children; k 1950 the corresponding figures 

for women 30-34 years of age were 17,3, 23.4, 

51.5,,, and 7.9 percent, respectively., 

The census data on children ever born are 

subject to some undercount. The Bureau does not 

ask single women about births. (For purposes of 

Table D. Children ever born per 1,000 women of childbearing age, by marital status: 

United States, 1950, 1957, 1960, and 1962 

Children per 1,000 total Children per 1,000 women women including single ever married 

Age of woman 

1962 1960 1957 1950 1962 1960 1957 1950 

15-19 years 105 127 108 105 702 792 672 604 

20-24 years 1,015 1,032 971 738 1,434 1,441 1>368 1,082 

25-29 years 2,092 2,006 1,900 1,436 2,318 2,241 2,139 1,654 

30-34 years 2,586 2,445 2,249 1,871 2,797 2,627 2,425 2,059 

35-39 years 2,664 2,523 2,457 2,061 2,812 2,686 2,612 2,247 

40-44 years 2,552 2,409 2,342 2,170 2,694 2,564 2,514 2,364 

10 
--------

1 

!

I the tabulations the single women are assumed to be 

I childless.) There is also some underreporting by 

women ever married. Data on retrospective birth 

rates for distant dates (such as the period 1930 

to 1934), obtained from fertility histories in 1959, 

show annual birth rates that run about 5 percent 

below those from contemporary vital statistics 

for white women and about 8 percent for nonwhite 

women. The census data include illegitimate births 

to the extent that such are reported by women who 

have married, but the vital statistics have more 

complete coverage of illegitimate births. 

Fertility histories obtained in 1959 provide 

direct evidence that recent marriage cohorts had 

more births earlier after marriage than some 

earlier cohorts. Figure 2 illustrates the rise in 

first birth rates at short intervals after marriage. 

The same survey (1959) shows that among 

white births in the period 1955 to 1959 the median 

spacing since first marriage of the mother was 

16.2 months for first births, 49.0 months for 

second births, 82.7 months for third births, and 

108.4 months for fourth births. The medians cited 

represent reductions of 4 to 6 months over the 

corresponding medians for white births in the 

period 1935 to 1939, The survey shows that roughly 

90 percent of first births occur by 5 years after 

the first marriage of the mother. Roughly 80 percent of births of second and higher order occur 

in the period 1 to 4 years afteq the birth of a 

previous child. The very high concentration of 

events within a narrow spacing range indicates 

that information on the number of women by interval since the latest birth would be of considerable 

value for improving short-run projections of 

births. 

Increases after 1940 in the fertility of women 

in various subgroups of the population have 

generally more than offset the effect of certain 

trends that might otherwise have caused some 

decline. For example, a trend toward increased 

urbanization of the population tended to cause some 

decline because urban fertility has been much 

lower than rural fertility, but this has been offset by a relatively larger rise in urban fertility 

than in rural fertility with the result that urbanrural differences in fertility have narrowed since 

1940. Another example is the trend toward increased educational attainment of the population 

qnd the tendency for the better-educated groups 

II _ Women Erst married !. 1950-54 

[ 

10 Women first mauled III t930-34# 

~
 t


oo~ 

MONTHS SINCE FIRST MARRIAGE 

- - SUUKLL Emerging Techniques In Population Research, 

1963. kfilbonk M8mor/ol Fund, w99, 

Figure 2. First births in successive months since


f~rst marriage per I,000 women chi IrJless at be­


glnni ng of the month, for specified marriage co­


horts of white women.


to have fewer children than the less-educated; 

this has been offset by a relatively larger rise in 

fertility among women at higher education levels. 

Comparisons of 1940 and 1950 census data indicate that shortly after World War II the population 

groups which previously had the lowest fertility 

had the most increase with the result that fertility differentials by social and economic status 

narrowed somewhat, Data from the 1960 census 

indicate, in general, a continuation of the trend 

although the relative increases in fertility were 

similar for many social and economic groups 

between 1950 and 1960. Except. at very young 

childbearing ages the fertility of the nonwhite 

population increased more than that of the white 

population between 1950 and 1960. 

Census data on “women by number of own 

children under 5 years of age in 1950 and 1960 

indicate that changes in the numbers of women at 

each age were such that there would have been a 

11

decline in the total number of own children under 

5 years had this not been offset by the effect of 

a rise in the proportion of women each age who 

had married and by higher fertility per evermarried woman of each age. The absolute number 

of own children under 5 years increased from 

15.6 million in 1950 to 19.5 million in 1960 for 

the conterminous United States. If only the numbers of women at each age had changed, there 

would have been a decline of about 0;5 million 

own children under 5 years. Increases in the 

proportion of women of each age who had married 

added an estimated 0.6 million own children under 

5 years to the population, and increases in the 

number of own children per woman ever married 

added 3.8 million. Thus, in terms of the data 

used, the rise in current fertility of the evermarried women was a more important component 

of change than the effect of different numbers of 

women at the two dates or of different proportions 

married. Other data and dates may yield quite 

different results. 

Annual data on the marital status of the 

population by age and sex from the Current Population Survey suggest that the trend toward 

relatively more married women at the young 

childbearing ages has halted, and, in fact, there 

is some evidence, not statistically significant 

so far, that a slight decline in proportion ever 

married has occurred for girls 14 to 17 years of 

age, especially among nonwhites. 

We may sum up the information presented 

above by stating that census data do not yet show 

any significant evidence of a decline in the average 

number of children ever born to women despite 

downward trends since 1955 or 1957 in such crude 

vital statistics measures as births per 1,000 

population or per 1,000 women of childbearing 

age. 

Prospects for Future Data 

A special report is available from the 1960 

census on women by number of children ever 

born in relation to many characteristics of the 

women and their families. The Bureau of the 

Census is exploring the possibility of obtaining 

funds from foundations and other government 

agencies for completing some of the other special 

1960 census reports the Bureau was unable to 

complete with decennial census funds. It has been 

successful in securing support for special tabulations on childspacing and on own children under 

5 years of age. The Bureau published some dat,~ 

on children ever b-n and on own children under 

5 years in Volume I of the 1960 Census of Po/Mlai%on, thereby making the data available for a 

wider variety of areas than ever before although 

these data were not cross-tabulated with social 

and economic characteristics such as will appear 

in the special reports. Data on children ever 

born were collected in the March 1962 Current 

Population Survey. 

The Bureau of the Census collected data in 

the summer of 1964 in the Current Population 

Survey on fertility by social and economic 

characteristics of women and their families; such 

information has not been obtained from surveys 

made during the 10 years after 1952. 

The Bureau probably will continue to ask 

questions on children ever born at 2- or 3-year 

intervals in the Current Population Survey. If 

there is sufficient demand, the Bureau may also 

obtain fertility histories every 5 years or so. 

The Bureau will continue to do research in 

the field of fertility although, like the National 

Center for Health Statistics, it is primarily a 

collector of basic data. Some of the materials may 

be used in a demographic model that is being 

developed by the Bureau, and some may be used 

in projections of population. 

CHAPTER Ill. PERIOD FERTILITY AND 

COHORT FERTILITY: THEIR 

MEASUREMENT AND INTERRELATION 

Fertility is generally discussed in two different ways: as the number of children born to a 

woman during her life and as the birth rate in a 

population during a year. An important measurement problem is the relationship between these 

two faces of fertility. 

Lifetime fertility can be measured through 

a continuing registration of the births that occur 

age by age to an aggregate of women born at the 

same time, called a birth cohort. To eliminate 

from the record the influence of mortality and 

migration on the size of the group, it is customary 

12 
to compute a separate birth rate for each age 

interval of experience. The set ofsuchbirthrates 

for all reproductive ages iscalled a cohort fertility-age function. The sum of these rates, called 

the cohort total fertility rate, gives the level of 

fertility. It is interpretable as the number of births 

to a thousand women—or whatever other base 

may be used for the component rates—during a 

lifetime (in abstraction from the selectivity of 

mortality and migration). 

The second view of fertility begins with the 

crude birth rate, the number of births in a 

particular year per 1,000 population. Since children are born only to women within the reproductive age span and differentially by age within 

this span,, the birth rate depends on the distribution 

of the population by age and sex. To provide a 

fertility record which is independent of this 

distribution, it is customary to compute separate 

birth rates for women of each age. The result, 

as before, is a fertility-age function, but this 

time for a period. The level of fertility in a 

period may be obtained by summation of the 

age-specific birth rates to give the period total 

fertility rate. 

The basic component of the period and cohort 

fertility-age functions is the same: the birth rate 

for women of a particular age and time. If such 

rates are shown in a table with years as columns 

and ages as rows, the rates in each column represent a period fertility-age function, while the rates 

in each diagonal (from upper left to lower right) 

represent a cohort fertility-age function because 

in each such diagonal, age and time increase 

@Yi pasw as they must for any cohort. Because 

period and cohort fertility-age functions are derived differently from the basic table of birth 

rates by age and time, their summary measures, 

such as the total fertility rates, are not generally 

the same. As a generalization, the relationship 

between period and cohort fertility rates depends 

on changes in the age distribution of cohort fertiIity. For example, if earlier cohorts concentrate 

their childbearing in older ages and later cohorts 

concentrate their childbearing in younger ages 

(i.e., if the mean age of cohort fertility declines), 

then period total fertility rates will be higher 

than cohort total fertility rates during that era 

because the components of period fertility consist 

of the relatively high birth rates at older ages of 

the earlier cohorts and the relatively high birth 

rates at younger ages of the later cohorts. 

In recent American reproductive history the 

time series of period and cohort total fertility 

rates have diverged both in the short run and in 

the long run. Short-run fluctuations of fertility 

from period to period are reflections of temporary 

disturbances of childbearing in response to experiences like war or depression. Since these 

affect all ages more or less, the period total 

fertility rate registers the impact immediately 

and directly and then a little later rebounds when 

the persons concerned recover the births which 

have been delayed. The participating cohorts show 

the marks of depression on their birth rates in 

the ages they occupied when it occurred and also 

the marks of recovery in subsequent ages. Thus, 

the fluctuation is observable for cohorts in a 

disturbance of the age distributions of their fertility without necessary changes in their total 

fertility rate. 

Underlying the fluctuations of the last few 

decades has been a persistent trend toward 

younger childbearing from cohort to cohort. This 

has had the consequence of distorting the period 

total fertility rates upward to give the spurious 

impression of a greater rise in cohort fertility 

than in fact occurred. Most of the rise in period 

fertility between the late 1930’s and the 1950’s 

is attributable to the trend toward younger childbearing from cohort to cohort. Thus, the period 

total fertility rate moves differently from the 

cohort total fertility rate when there is either a 

long-run evolution or a short-run disturbance 

of the age distribution of cohort” childbearing. 

The relationship between the number of 

children a woman has during her life and the 

annual birth rate may be summarized under two 

headings: changes in the age pattern of cohort 

fertility, which determine the relationship between 

time series of the cohort total fertility rate and 

the period total fertility rate, and changes in the 

age distribution of the p~pulation, which determine 

the relationship between time series of the period 

total fertility rate and the crude birth rate. The 

crude birth rate is a weighted average of the agespecific birth rates which constitute the period 

total fertility rate, the weights being the proportions of the population that are females in the 

various ages of reproduction. These proportions 

13 
respond to all influences on the age structure, but, 

in particular, to the movements of the birth rate 

a generation before, because they determine the 

size and age structure of the group of persons 

currently bearing children. A decline in the birth 

rate a generation earlier will tend to make the 

current birth rate decline relative to the period 

total fertility rate and conversely for a rise. 

Since the crude birth rate in the United States 

has experienced many changes in recent history, 

the prospect is that the crude birth rate and the 

period total fertility rate will move differently 

for many years to come. Since short-run and 

long-run changes in the ages at which cohorts 

bear children are also not unlikely, it is clear 

that movements of the crude birth rate will continue to be misleading clues to the trend in cohort 

fertility. 

In attempting to determine the trend in cohort fertility for recent years, appropriate control 

of the influence of the changing age distribution 

of the population can be made by studying period 

fertility-age functions, but no way exists of 

handling the current relationships between period 

and cohort measures. The problem is that the 

cohorts which are the major contributors to contemporary fertility will not reach the end of their 

reproductive span for many years. Not only do 

their total fertility rates remain unknown in the 

meanwhile, but the changing age pattern of their 

fertility remains unknown also, and without tie 

latter information it is impossible to determine 

the extent to which current period total fertility 

rates are giving a distorted picture of underlying cohort fertility. For example, the period 

total fertility rate for the United States declined 

from 1957 to 1963. Among the possible interpretations of this movement is a decline in 

cohort total fertility or a rise in the mean age of 

cohort fertility. Only the passage of time can 

provide the data required to translate movement 

of the period total fertility rate into statements 

alxmt the exact trend in cohort fertility. 

Beyond the level of fertility measures based 

on age-specific birth rates, it is feasible, using 

appropriate registration and enumeration data, to 

determine birth rates in each age group and time 

period separately for women of the different 

parities, i.e., in terms of the numbers of previous 

births to them. This addition of parity detail to 

the information about the level of fertility age by 

age is a valuable contribution to an inquiry into 

the sources of observed changes in fertility, but 

it does not resolve the question Of the relationship between period and cohort total fertility 

rates, which is the crux of the determination of 

the contemporary trend in fertility. Thus, from 

a period standpoint any age-specific birth rate 

is a product-sum of the proportions of women 

in the age group in each parity and their respective parity-specific birth rates. The birth 

rate in the age group changes from year to year 

in part because the parity distribution of tht! group 

likewise changes and that parity distribution reflects the previous reproductive histories of the 

women concerned. In the study of fertility fluctuations relative to movements of socioeconomic 

indexes, for example, it is desirable to remove 

from the fertility measurements whatever may 

be ascribable to the fertility of previous years, 

and this is accomplished by parity-specificity, 

Similarly, the enlargement of the detail about cohort fertility histories to encompass the changing 

parity distribution year by year makes it possible 

to identify the sources of past modifications of the 

level and age distribution of childbearing within 

the separate parities as well as ages. But there 

is nothing about this procedure which helps to 

solve the problem of the distortion of cohort 

measures by period measures. 

The conclusion reached for measurements 

based on parity-specificity applies with equal 

force to all attempts to make the fertility process 

more specific. From appropriate registration 

and enumeration data birth rates may be constructed which are, for example, specific for the 

number of years married or for the number of 

years since the previous birth (so-called durationspecific or interval-specific rates). These make 

possible more refined discrimination of periodspecific perturbations and enlarge the detail of 

knowledge about the changing patterns of cohort 

childbearing, but they are inherently incapable of 

providing reliable predictions about the subsequent fertility of cohorts of women who are 

currently in the childbearing ages, and this is 

what is required to make an exact statement now 

about the current trend in fertility. One further 

source of information which may help answer 

this question, based on reports of women in the 

childbearing ages concerning the children they 

expect to have, is discussed later in this report, 

14 
CHAPTER IV. EVIDENCE OF 

CHANGE IN CURRENT FERTILITY 

Changes in cohort Fertility 

Figure 3 shows the average number of children ever born per 1,000 women (i.e., cumulative 

birth rates) by exact ages 20, 25, 30, 35, and 50 

years for cohorts of women born every fifth year 

from 1878 to 1943. The broken lines for age 50. 

years (when childbearing is assumed to be complete) are projections based in part on the number 

of births expected by a national sample of wives 

in the childbearing period, interviewed in 1960.1 

These expectations suggest that complete fertility 

is approaching an upper limit of about 3,100-3,400 

births per 1,000 women for the cohorts of the 

early 1930’s. More recent cohorts (specifically 

those of 1936-42) expect fewer children than those 

of 1931-35; this may mean that the trend toward 

higher fertility will cease or reverse. 

Suggestive evidence that completed fertility 

will stabilize or decline is provided by comparisons among interview surveys of three 

independent samples of white wives 18 to 39 years 

of age, conducted in 1955, 1960, and 1962. In each 

of these surveys the wives were asked how many 

births they thought they would have altogether. 

The results are presented in table-E for four age 

groups. (The average numbers of births in table 

E are not comparable with those shown in figure 

3 because the former relate to white married 

women and the latter to all women.) A comparison between ages 18-24 years and 25-29 years 

in the 1960 and 1962 studies shows that the younger 

group expects about 10 percent fewer children 

than the older. Since there may be some tendency 

for expectations to increase with age, however, 

it is more valid to make intercohort comparisons 

at the same ages for different dates. The use of 

this procedure does not suggest as sharp a decline 

in completed fertility (Compare births expected 

by wives 18-24 years in 1955, 1960, and 1962.), 

but it does indicate the likelihood that the completed fertility of the cohorts born in the late 

1930’s and early 1940’s will be equal to or below 

that of the cohorts of the early 1930’s. 

The number of children ever born by age 20 

years has already fallen slightly between the 

“’ooo~ I 

W&zz!
 187s 1883 1888 1893 1898 1903 1908 1913 1918 !923 1928 1933 1938 1943 50:

Figure 3. Number of children ever born per I?COO


women, by exact age specified, for every fifth


cohort from 1878 to 19!3.


cohorts of 1938 and 1943 (a decline which occurred 

between 1958 and 1963). This does not mean that 

the 1943 cohort will necessarily have fewer children than the 1938 cohort, but it is consistent 

with the prospective stability or decline in completed fertility. 

Fe upward trend in births by age 25 years 

has not yet reversed direction, but it has slowed 

down, as is shown in figure 3. This also may be 

taken as an indication that cumulative fertility 

rates are approaching upper limits. 

Another important cohort trend is the tendency for couples to have more of their children 

while the mother is still in the early part of the 

childbearing period. The proportion of children 

born before the mother’s thirtieth birthday, for 

example, was 65 percent for the 1913 cohort and 

78-85 percent for the 1933 cohort (depending on 

how many births these women have altogether). 

15

--------

--------

--------

Table E. Average number of births expected, by wife’s age,for couples with white wives€

18-39 years of age: United States, 1955, 1960, and 1962€

Cohorts to which rates relate€

Wife’s age 1955 1960 1962


1955 1960 1962


18-24 years-------- 3.2 3,0 3.1 1931-37 1936-42 1938-44 

25-29 years 3.4 1926-30 1931-35 1933-37 

30-34 years ::: u 3.2 1921-25 1926-30 1928-32 

35-39 years 2.9 3.0 2.9 1916-20 1921-25 1923-27 

source: Freedman, R., Goldberg, D., and slee.inger,D. p.: current fertility expecta-€

tions of married couples in the United States. Population Index 29(4):369, Oct. 1963.


The trend toward younger childbearing has 

been closely associated with a trend toward 

earlier marriage. The proportion ofwomen who 

were married byage20 years, for example, was 

between 37 and 40 percent before World WarH 

according to the 1920, 1930, and 1940 Census 

of Population. After the war, however, the proportion ever married by age 20 years rose to 

50 percent in1950 andto54percent in1960. This 

trend kan also be seen in the proportion ever 

married by age 25 years: 71-72percentduringthe 

interwar period, 83 percentby 1950, and87 percent by 1960. The tendency toward earlier marriage would have brought about ayounger age at 

childbirth even iftherehad beenno change in the 

timing of births within marriage. Butitis also 

evident that postwar children were born with 

less delay after marriage than previously.2 Together these trends reduced age at childbearing 

greatly. 

The tendencies toward higher completed 

fertility and younger age at childbirth raised the 

birth rates at younger ages greatly. The number 

of births per 1,000 women during ages 20-24 

years, for example,was 615forthe1913cohort 

(during1933-37)and 1,207for the 1933 cohort 

(during1953-57). Withoutthetrendtoward€ younger

age at childbirth€ the ratefor the lattercohort€

would have beenbetween810and 890ratherthan€

1,207.Thus, birthratesin therecentpasthave€

been highnot onlybecausecoupleswere having€

larger families but also because they have been 

marrying younger and having ahigher proportion 

of their children while the mother is young. It 

now seems likely that this trend toward younger 

childbearingis also reaching a limit. 

Most of the births that have brought aboutthe 

rise in average numberof children ever bornand 

the trend toward youngerchildbearing occurredin 

the 15-year period during 1948-62. (This period 

is indicated in figure3 by the arrows for January 

1, 1948 and 1963, which point at the cumulative 

rates achieved by these dates.) In theyearsahead 

two different cohort tendencies will dominate 

period fertility rates. First, as noted before, completed fertility willprobabl yleveloff forthe cohorts born in the late 1930’s and afterwards and 

may decline; this means stability or decline in 

rates at the younger ages. Secondly, very high 

birth rates attheyounger ages mean lower birth 

rates at the older ages. Again comparing the experienceof the 1913 and 1933 cohorts, theearlier 

group had 841 births per 1,000 women after age 

30 years, but the more recent cohort will have 

750 at most (if, as seems unlikely, maximum 

birth expectations are realized) and may have as 

few as 450. 

In summary, cohort trends together with expectations data strongly suggest stability or decline in age-specific birth rates at the younger 

childbearing, ages and decline at the older ages. 

16

------------------------

------------------------

------------------------

------------------------

------------------------

------------------------

Changes in Period Fertility 

Between 1957 and 1963 the crude birth rate 

dropped from 25.3 to 21.7, a reduction of 14 percent. Whelpton has shown that this decline was 

due partly to changes in the age composition of 

the population and partly to lower age-specific 

birth rates.3 

The age-specific birth rates for 1957 and 

1~6~, shown in table F, reflect the cohort changes 

discussed above. The 1962 rates are down at the 

younger ages (especially at ages 15-19 years); 

this is consistent with the leveling off or reduction of completed fertility in the cohorts of 

1Q38-47. They are also down at the. older ages 

as a result of the concentration of childbearing 

at younger ages, 

The outlook for period fertility rates during 

the remainder of this decade is that age-specific 

birth rates above age 30 years will continue to 

decline and that rates below age 30 may decline 

or stabilize at approximately their current levels 

(which are very high relative to the prewar period). 

It does not seem probable that age-specific birth 

rates will increase although the rates at younger 

ages would increase if completed fertility were to 

rise to 3,400 (or more) births per 1,000 women 

and if the trend toward younger childbearing were 

to continue. Both possibilities now seem unlikely. 

Although age-specific birth rates are expected to stabilize or decline, the annual number 

of births may tend to rise. This is due to increases in the number of women at the younger 

childbearing ages. These increases resulted from 

the increase in the number of births that occurred 

after World War II. The prospective trend in the 

number of women 18-29 years of age is as follows: 

Estimated numbev of 

women 18-29 years 

Year on July 14 

1960 ------------- 13,910,000 

1965 ------------- 15,958,000 

1970 ------------- 19,232,000 

These projections show an increase of 38 

percent in this age group in 10 years. 

A set of population projections prepared by 

the Scripps Foundation shows that moderately 

lower age-specific birth rates together with 

higher numbers of women would maintain the crude 

birth rate at approximately the current level of 

22 per 1,000 for the remainder of the 1960’s. 

These projections also show that a substantial 

decline in completed fertility and a trend toward 

later childbearing could lower the annual crude 

birth rate for the period 1965-70 to 19 per 1,000. 

In contrast a continuation of the rise in completed 

fertility and of the trend toward earlier childbearing could raise the birth rate in 1965-70 

to 26 per 1,000. At present the assumptions that 

would bring about either the high or low extreme 

do not appear to be likely. 

Table F. Estimated age-specific birth rates for all women: 1957 and 1962 

Woman’s age 

15-19 years 

20-24 years

25-29 years 

30-34 years 

35-39 years 

40-44 years 

Source: Estimated by the 

Cohorts to which 

rates relate 

1957 1962 Percent 

change 

1957 1962 

97.9 83.9 -14 1938-42 1943-47 

257.2 243.2 -5 1933-37 1938-42 

195.8 191.2 -2 1928-32 1933-37 

116.8 107.4 -8 1923-27 1928-32 

59.8 53.0 -11 1918-22 1923-27 

15.4 14.8 -4 1913-17 1918-22 

Scripps Foundation for Research in Population Problems. 

17

The Relationship Between Fertility 

Trends and Economic Conditions 

lhere is much concern about the social and 

economic causes of recent fertility trends in this 

country. Has the high fertility of the postwar 

period been due, at least in part, to relatively 

good economic conditions? Before we can begin 

to answer this question, we must again distinguish 

between the period and cohort approaches to the 

study of fertility. 

So far the available evidence shows that 

marriage rates and period fertility rates are 

affected by economic conditions, that is, birth 

rates change from year to year partly in response 

to changes in economic conditions as measured 

by indexes of unemployment, income, and industrial production.b Evidently more couples 

marry and more married couples try to have 

children when economic conditions are good. 

Mar?iages and births are often postponed under 

less favorable circumstances. 

However, there is as yet no evidence that 

the total number of children couples have is influenced by economic conditions per se. This 

conclusion is based on a study of the relationship between the completed fertility of cohorts 

and measures of the economic conditions prevailing while those cohorts were in the most 

fertile years of the childbearing period.d This 

study shows that completed fertility dropped 

steadily up to the 1909 cohorts in spite of rapidly 

improving economic conditions. The upturn in 

completed fertility began with the 1910 cohort 

and was continued by later cohorts. Yet the 1910 

cohort spent the highly reproductive ages 20-29 

years in the decade of the 1930’s. The 1912 cohort was hit hardest during the high-fertility 

years of life; these women reached age 18 years 

in 1930; yet they had as many births by the end 

of the childbearing period as the women of the 

1906 cohort, who spent ages 18-24 years in the 

relatively prosperous 1920’s. Thus, it does not 

seem likely that completed fertility has been 

influenced discernibly by changing economic conditions. It is possible that some other aspect of 

‘This study was conducted at the Scripps Foundation for 

Researchin PopulationProblems. 

our changing economy affected couples’ desires 

for children. Obviously the shift away from childless and one-child families (which is an important 

part of the trend that is expressed by the upward 

movement of completed fertility rates) is strong 

and widespread. It must be related to some equally 

impressive changes in our culture, and these 

changes may well be related to economic trends 

even though they are not measured by the commonly used indexes of economic conditions. However, we have not yet established what they are. 

CHAPTER V. THE SURVEY AS 

A SOURCE OF FERTILITY DATA 

Beginning with the Indianapolis Study of 1941, 

the interview survey has become an important 

source of information on fertility in the United 

States. This instrument of research has helped 

us to measure aspects of fertility, such as the 

timing of births, that have not been available from 

birth registration and the decennial census, and 

it has also increased our knowledge of many 

factors influencing trends and differentials in 

fertility. 

Two kinds of fertility surveys have been 

conducted in the United States. First, there are 

surveys designed primarily to test hypotheses 

about the relationship between fertility and social 

and psychological variables. Examples of these 

are the Indianapolis Study of 1941,7 the Princeton 

Study (a panel survey begun in 1957) ,gand the 

Detroit Area Study (D.A .S.) of 1962} 

The second type of survey is designed primarily to describe the distribution of fertility 

variables in the country as a whole and to show 

how these variables differ and change for broad 

segments of the population. ExampIes of these 

are the Growth of American Families (G.A .F.) 

Studies of 1955 and 196010 and the national surveys of the University of Michigan’s Survey Research Center, which include questions on past 

and expected childbearing! 1Another important 

descriptive survey is conducted about once every 

2 years as part of the Census Bureau’s Current 

Population Survey. 12 It is designed to get current 

information on the number of children ever born 

18

to women ever married and sometimes on the 

spacing of these births. 

During the past 10 years it has become increasingly evident that the survey can be used 

to expand greatly the variety of fertility data 

typically available from government agencies. 

The specialized surveys have obtained a wealth 

of material which should aid in the assessment of 

current and future fertility trends—expectations 

data, ideals, preference orders, impairments to 

reproduction, and methods of family limitation. 

All of these data have been collected with no indication of a negative response on the part of the 

people who were interviewed. In fact, response 

rates for the fertility studies have been exceptionally high.e Data on number of children expected 

as well as other kinds of fertility data made 

available through the surveys should be sensitive 

to changes in cohort behavior, probably more 

sensitive than a continued refinement of conventional data. For example, 1955-57 age-specific 

birth rates for all women imply a total fertility 

of about 3.7 children per woman; yet there is 

nothing in the survey data collected from married 

women to suggest that any national cohort will 

approach that level. 

Many of the subjects covered in the specialized fertility surveys are probably best left to 

university-based, research organizations. This 

is particularly true of many topics included in 

surveys designed to probe deeply for the social 

and psychological factors underlying trends and 

differentials in fertility. It may also be true of 

information of a more personal nature, such as 

impairments of the reproductive system and 

methods of family limitation. Even these subjects may eventually be considered proper subjects of government inquiry, inasmuch as they 

are related to health. 

However, there are certain subjects which 

should be covered on a regular basis and may be 

considered appropriate for government-sponsored surveys. One of these has already been 

mentioned: the number of children ever born, 

which is provided by the Census Bureau on an 

“For example,the 1955 G..4.F. Study and the 1962 D,A.S. 

both resulted in the completion of between 91 and 92 percent 

of the interview with eligible response. hloreover, questions 

dwding with fertility and matters related to fertility had respense rates as high as or higher than typical socioeconomic 

questions. 

intermittent basis. Another is the number of 

children expected. 

Questions about the number of children expected were first used on a nationwide scale in 

the Growth of American Families Study of 1955. 

Each wife in the sample was asked whether or not 

she thought she could have more children and if 

she could how many she thought she would have. 

There was, of course, some justifiable skepticism 

about the accuracy of the wives’ replies to such 

questions, and a 1960 survey was conducted partly 

in order to evaluate the 1955 statements. The 

1960 Study did not deal with the same wives as 

the 1955 Study but with women who had the same 

characteristics. In other words, the 1960 survey 

was designed to see whether or not wives could 

predict accurately the number of children that 

women like themselves would have. 

As far as the average number of children born 

in a 5-year period is concerned, the replies of 

the 1955 wives were amazingly accurate. The 

nonsterile wives in this survey expected an 

average of 0.8 children in 1955-60, and comparable wives in the 1960 Study reported that they 

had borne an average of 0.8 children. Even more 

surprising is the fact that the predicted and actual 

distributions of women by number of children 

born in 1955-60 are not significantly different. 

This is shown in table G. 

This surprising accuracy of the aggregated 

replies of a large group of women does not result from a high degree of accuracy for individual 

women. Many women undoubtedly had more children than they expected, and many had fewer. But 

these deviations appear to be due to accidental 

factors (unintended pregnancies and unforeseen 

fecundity impairments) that tend to cancel each 

other’s effects. 

Other studies suppmt the idea that aggregate 

predictions of future fertility based on expectations data are accurate. Westoff, Mishler, 

and Kelly found that statements of desired family 

size at time of engagement and completed fertility some 20 years later for a panel of 145 

fecund, predominantly college-educated, Protestant couples differed by less than 4 percent.i3 In 

Detroit between 1955 and 1958 the substantial 

change in the economic conditions of that community did not affect the expectations of a panel 

of 237 women. At the beginning of the period they 

19 
--------------- -------------- ----

----------------------

Table G. Percent distribution by number of births in 1955-60 expected by nonsterile


wives in 1955 and reported by comparable wives in 1960: Growth of American Families


Study.


Percentage expecting specified


number of births in 1955-60 Percentage


(from 1955 Study) having specified


Number of births number of births


in 1955-60 (from


Minimum number Maximum number 1960 Study)


Total------------------------


None----------------


One------- ---.---


Two--------------------------------


Three------------------------------
 Four+--------


expected expected


100 100 100 

52 52 50 

25 24 28 

17 18 16 

5 5 5 

1 1 1 

Source: Campbell. A. A., Whelpton, P. K., and Tomasson, R. F.: The Reliability of


birth expectat&s of U.S. wives.- Proceedin~s of the Inte~ational Population Confer­
 ence. New York, 1961, Volume I. London. John Wright and Sons, Ltd., 1963. pp. 49-58.


collectively expectedto have an additional
176 

children. When reinterviewedin1958,thissample


of women had givenbirthto84 childrenand ex-


pected94 more—a totaldifference
 oftwoexpected


births,or lessthan.Olper woman.14 Similarly,


afteran intervalof 3 years reinterviews
with


905 two-parity
women inthePrincetonStudyre­


vealed a change of less than 1 percentinthe


desirednumber ofchildren~5


The relativestability of expectations
 data


overvaryingperiodsoftime doesnotnecessarily


applytoallidentifiable subpopulations
 withinthe


samples mentionedalmve.For example,acom­


parisonofthe1955and1960 GrowthofAmerican


Families data revealsa small but significant


increasein expectedfamilysizeas the cohort


ages.16 Mether thisisageneralphenomenonor


a characteristic
 of theperiodbeingexaminedis


undetermined.Anotheranalysisofcohortchanges


inexpectedfamilysizeovertime (1955-62)
indi­


cates thatincreasesin cohortexpectation
with


increasesin age are entirely attributable
 tothe


behaviorof Catholiccohorts.The Catholicco-


hortsof 1926-37increasedtheirexpectations
 by


about10percentaccordingtoresultsfrom rela-


tively
smallsamplescoveringthe7-yearinterval


being studied.In contrastto the instability
 of

Catholiccohortscomparable non-Catholicco-


hortsremained exceptionally consistent
 intheir


expectations
 .17


Although particularsubgroups withinthe


population may be unabletopredict
heireventual


fertility
 withgreataccuracy,itcanbe regarded


as well-established that,intheaggregate,
wives’


predictions of theireventual
number ofchildren


do bear some relationship to reality,
and it


appearsnowto be a fairly
closerelationship.l%e


collection of more dataon childbearing
 expecta­


tionsisrequiredtoseehow wellgroupsofwives


are able to predictfertility
 over an extended


periodoftime andto establish
 thegeneralnature


ofthemodifications
 thathaveto be madeto these


data.Inotherwords,birthexpectations
 areneeded


at fairlyregularintervals—perhaps
onceevery


5 years from a largenationwidesample.The


Subcommittee hopes thatsome agency of the


governmentwillregard birthexpectations
 asan


appropriate
subjectofinquiryon a regularbasis.


The Census Bureau’sCurrentPopulation
Survey


isideally suitedtothistask.
f

‘.Although a time series of national expectations datn is 

available from annual studies conducted by the Survey ltl Isearch Center, the sample size is too small to analyze rr.l]nbly 

the birth expectations of selected key groups-women under 

25 years or nonwhites, for example. 

20 
It is true that completed fertility changes, 

but it does not change rapidly nor does it behave 

erratically. For example, the average change 

between one cohort and another in the cumulative 

number of children born by age 40 years (when 

fertility is nearly complete) has been only 1.6 

percent (cohorts of 1877-1923). The main point 

is that fertility values are embedded in a cultural 

context which changes slowly, and these values 

are the most important determinant of the number 

of children expected and the number actually born. 

There is good reason to believe that birth 

expectations can assist in observing important 

trends that are beginning to develop before these 

trends can be identified in current birth statistics. 

On the basis of data collected in 1960 and 1962, 

it appears that the completed fertility of the cohorts of 1936-40 will be equal to or below the 

completed fertility of the cohorts of 1931-35. 

Yet by 1960 the 1936-40 cohorts had borne 13 

percent more children by ages 20-24 years than 

the earlier group had borne by the same ages. 

It will not be possible to use numbers of registered 

births to” estimate the final number of children 

borne by both of these cohort groups until about 

1975, when the 1936-40 group will be 35-39 years 

of age. In other words, data on expectations may 

have indicated a turning point 15 years earlier 

than it would have been recognized safely from 

numbers of registered births. It maybe concluded 

that the use of expectations data to project trends 

in completed fertility is well worth continued investigation on a large scale and that the necessary 

information can best be collected through university-based, research organizations supplemented 

by occasional surveys sponsored by a government 

agent y. 

CHAPTER V1. 

FERTILITY CHANGES—IMPLICATIONS 

FOR POPULATION PROJECTIONS 

Estimates of future population are essential 

to national planning in all its ramifications. It is 

therefore important that methods of preparing 

population projections, by various characteristics, be improved. The failure of earlier projections to predict population accurately or to 

offer a sufficiently narrow range to be practical 

should be a spur to further effort. 

Projections of population generally have been 

made either by some type of mathematical extrapolation of the total population or by the application of projected age-specific birth and 

death rates to the population or to separate 

segments of it. They generally carry stated 

assumptions regarding gains or losses through 

migration. 

Since births are the principal variable in 

national population projections (death rates being 

fairly constant and at low levels and immigration 

being rather small in volume in the United States), 

measurements of fertility that are relevant to the 

prediction of the future level of births are of 

practical importance. It is well, then, in assessing 

the measurement of fertility to consider the 

status of fertility projections at present and what 

is needed to improve them. 

Activity in the Field of Projections 

The first official projections based on agespecific rates were made under the auspices of 

the National Resources Committee by Thompson 

and Whelpton in 1938. Next, detailed projections 

with considerable analytical detail were prepared 

under the auspices of the Bureau of the Census by 

Whelpton, Eldridge, and Siegel in 1947. The Census 

Bureau has since revised the projections periodically. It is now preparing extensive revisions of 

its projections of 1958. 

Another set of birth projections has developed 

from the first, or 1955, survey of the Growth of 

American Families Study-a joint project of the 

Scripps Foundation for Research in Population 

Problems at Miami University at Oxford, Ohio, 

and the Survey Research Center at the University 

of Michigan. These projections are based upon 

an artful interweaving of birth cohort fertility 

data with data concerning number of births expected, described in previous paragraphs. A 

second survey in 1960 provided at once an evaluation of the method and a basis for revising the 

data. 

There are besides these formal sets of projections a number of projects testing methods of 

projections. Several years age Waggoner and 

Schachter (both then with the National Office of 

Vital Statistics) and Whelpton published projections made by extrapolating age-parity-specific 

rates. GrabilI of the Census Bureau has recently 

21 
made projections by the marriage-parity progression method. Both Ryder at the University of 

Wisconsin and Lawrence of the Census Bureau 

have been studying mathematical relationships in 

cohort fertility to find ways of extrapolating future 

fertility. Other experimentation is being done in 

the National Center for Health Statistics and in 

the Estimates and Projections Branch of the 

Bureau of the Census. 

Closely related to population projections are 

the demographic models. They utilize the same 

variables and much the same data input, but they 

are designed mainly to study the interaction of the 

demographic variables as such rather than to 

predict the future. Thus, instead of designing the 

model to use the data available, the input is 

tailored to fit the model. Although the models are 

useful in developing methodology, they are not 

capable as yet of producing realistic projections. 

Orcutt and his colleagues at the Universitjj of 

Wisconsin have devised a demographic model as 

part of a larger socioeconomic model. More 

recently Brunsman at the Bureau of the Census 

has undertaken the design of another model. 

In summary, there is considerable activity 

in population projections, but the efforts have been 

diffuse, and there is need for more concerted 

effort on this problem. 

Problems in Methodology 

Improvements in the measurement of fertility 

in the last decade have opened the way to improvements in the forecasting of births. There 

is a need for further research into the methodology underlying projections if the potentialities 

of the new information are to be realized. Some 

of the directions that need to be explored may be 

pointed out. 

More needs to be done in working out the 

relationship of cohort and period rates. An important innovation of the past decade has been to 

adjust age-specific rates to completed fertility 

by cohort. Since completed cohort fertility is 

more stable than period fertility and reflects the 

experience of actual women (though with important limitations), projections based on cohorts 

should be more accurate and have a narrower 

range of variation than those made by extrapolating period rates. However, there are pitfalls 

in the use of cohort analysis to project births. It 

is period fertility, not cohort fertility, that needs 

ultimately to be projected. Cohort rates must be 

converted to period rates before they can be used 

to project births, and the period rates must not I 

In projections made by extrapolating period 

rates, the assumption regarding the distribution 

of births by age of mother has little impact on 

the results. In projections made by cohort, even 

seemingly small differences in age distribution 

may have a major impact on the resulting period 

fertility. Variations in age have a long-run effect 

arising from the change in the length of a generation. They also have a short-run effect which 

arises from the change in the age distribution 

of mothers from one cohort to another and causes 

an overlapping or fanning out of fertility between 

successive cohorts. Stated in another way, borrowing is implicit in any assumption made regarding age of mother. The importance of age of 

mother may be appreciated if one considers that 

according to Whelpton change in timing of births 

was more important than change in expected size 

of family in explaining the high fertility of the 

1950’s. A shift in the pattern of timing of births 

from that of the cohort born in 1935 back to that 

born in 1915 would decrease the Nation’s births 

by some 7 million in the next 20 years (more 

in the long run) even if there were no increase in 

average lifetime number of births per woman. 

There has been considerable controversy as 

to whether or not the basic assumptions regarding 

cohort fertility should be based on extrapolation 

of past trends or on the expressed expectations 

of women as derived from a survey such as the 

Growth of American Families Study. Although the 

results of the survey should certainly be taken 

into account, its usefulness is somewhat limited, 

since the survey cannot cover women not yet of 

childbearing age and in a very few years it will 

be they who will be bearing most of the children. 

Even if survey results are used to establish the 

level of completed fertility, it may be desirable 

to use past experience to determine the timing 

of births as the Scripps Foundation has done in 

its projections. 

A further problem in the application of cohort fertility is in the splicing of future fertility 

with past fertility. Period rates derived from 

cohort rates may show sharp discontinuities between past and future unless there is an arbitrary 

22 
provision to assure smoothness. Period rates 

of the past have not shown sharp discontinuities 

from one year to the next except in unusual circumstances such as that of the postwar year of 

19460 It would seem reasonable to reject models 

of future fertility which imply precipitous declines 

in fertility in a short period, such as a single year. 

No project for making birth projections now 

takes account of all the variables which.have been 

shown to have a bearing on the level of fertility 

and for which data are available. It would be 

desirable to devise a method which would take 

account of all important variables if only to 

prevent incongruities that may be implicit in 

assumptions. A fully articulated methodology 

would account for at least the following variables: 

completed fertility, age of mother, marital status, 

parity of mother, and birth interval. The cohort 

fertility projections of the Growth of American 

Families Study took account only of completed 

fertility, age, and marital status. The marriageparity progression method does take account of 

parity and interval as well as marital status but 

at present disregards completed fertility and has 

only indirect control on age. The sheer magnitude 

of the computations has been a hindrance to complex models in the past, but the availability of 

computers and of the condensed languages for 

programming should now make them practicable. 

Working out meaningful relationships among 

all five variables would require cross-tabulations 

of a large body of data to assure that the differences between cells are statistically significant. Anything less than the 5 percent sample of 

the 1960 census would be too small. To enhance 

the quality of population projections for the next 

decade, it is highly desirable that the program 

for tabulating fertility data from the 1960 census 

be carried out. 

It has long been hoped that in making birth 

projections social and economic variables as well 

as the purely demographic ones might be taken 

into account. Projections of economic variabIes 

might well be included in the equation for birth 

projections, but at present there is no series 

suitable to the purpose. Economic projections 

today cover either only a year or two in the future 

or the long-term trends. The level of births is not 

well correlated with the long-range economic 

trend, and, although it does respond to annual 

changes in the level of economy, the fluctuations 

are too narrow to affect the size and composition 

of the population to any significant degree. The 

business cycles of 5 to 10 years’ duration appear 

to be the ones that influence fertility. But the 

economists have no projections of the business 

cycle. George Stolnitz at the University of 

Indiana has proposed that several series of projections be prepared under alternative assumptions respecting the level of the economy for the 

next 10 years. These projections would be used 

only to assess the consequences of possible 

change in the level of the economy and would not 

be given general circulation. 

Social variables are even less amenable to 

quantitative treatment than are economic variables. But since the relationship between the 

level of fertility and such factors as urbanization, 

educational level, and the rationalization of family 

planning have been established from census data 

and from studies like the Indianapolis, Growth of 

American Families, and Family Growth in Metropolitan America projects, trends in these factors 

might well be taken into account, at least subjectively, in establishing the assumptions regarding the ultimate level of fertility. More use 

should be made of the comparative fertility experience of other countries. 

23 
REFERENCES


10bserved cumulative birth rates are from National Office 

of Vital Statistics, Fertility tables for birth cohorts of American women, part 1, by P. K. Whelptmn and A. A. Campbell, 

Vita? Statistics–S’ps ciaJ Repmts, Vol. 51, No. 1,Public Health 

Service, Washington, D. C., Jan. 1960. The rates for 1S!63 

were prepared by the Scripps Foundation for Research in Copulation Problems. The projections of completed birth rates by 

age 50 years are derived from projection prepared by P. K. 

Whelpton and shown in Why did the United States’ crude birth 

rate decline during 1957-1962?, by P. K. Whelpton, Population 

Index 29(2):123, Apr. 1963. 

2Whelpton, P. K.: Trends and differentials in the epacing 

of birth. Demography 1(1):83-93, 1964. 

3Whelpton, P. K.: Why did the United States’ crude birth 

rate decline during 1957-1962? Population Index 29(2):120-125, 

Apr. 1963. Note: In this article the crude rate of 22.4 for 1962 

was designated as “Provisional. ” The subsequently published 

final rate was 22.4 for 1962 and 21.7 for 1963 (not corrected 

for c~pletenese of registration in either case). 

4Freedman, R., Whelp~rr, P. K., and Campbell, A. A.: 

Famiiy Planning, Sterility, and Population Growth. New York. 

McGraw-Hill Book Co., 1959. p. 390. 

5T0 be published. 

6See, for example, Birth rates and the interwar business 

cycles, by V. L. Galbraith and D. S. Thomas, J. Am. S;atist. 

A. 36(216):465-476, Dec. 1941; The influence of business 

cycles on marriage and birth rates, by D. Kirk, Demographic 

and Economic Change in Developed Countries, Princeton, 

Princeton University Press, 1960, pp. 241-260; National Bureau of Economic Research, Inc., The American baby boom in 

historical perspective, by R. A. Easterline, Occasional Pape~ 

79, New York, 1962. 

7Whelpton, P. K., and Kiser, C. V. (eds.): Social and psychological factors affecting fertility. Mi2bank Mern. Fund 

Quart. 21(3):221-280, July 1943; 22(1):72-105, Jan. 194* 

23(3):254-296, hdy 1945; 23(4):386-409, oqt. 1945; 24(1):49-

93, Jan. 1946. 

8Wes~ff, C. F., and others: Family Growth in Metropolitan 

America. Princeton. Princeton University Prees, 1961; Westoff, C. F., Potter, R. G., and Sagi, P. C.: The Third Child. 

Princeton. Princeton University Press, 1963. 

9For som,e preliminary results of this study see %n@ np 

placations of unfolding theory to fertility analysis, by D. Goldberg and C. Coombs, Emerging Techniques in Population R,,. 

search, New York, Milbank Memorial Fund, 1963, pp. 105-129 

Use of telephone interviews in a longitudinal fertility sturf~ 

by C. Coombs and R. Freedman, to be published in PublIt 

Opinion @arterly, spring 1964. 

10 Freedman, R., Whelpton, P. K., and Campbell, A. A.: 

Op. cit. The volume describing the results of the 1960 Study 

has not yet been published. Some preliminary reeults are reported by Campbell, A. A., Whelpton, P. K., and Toruasson, 

FL F., The reliability of birth expectations of U.S. wives, Pr{Jceedings of the [nteraational Population Conference, Nero York, 

1961, Volume I. London. John Wright and Sons, Ltd., 1963. 

rm. 49-58. 

llAxelrod, M., and others: Fertility expectations of thr 

United States population: A time series. Population Index 

99:25-31, Jan. 1963; Freedman, R., Goldberg, D,, and Slesinger, D.: Current fertility expectations of married couples in 

the United Statee. Population Index 29(4):366-391, Oct. 196X. 

12U.S. Bureau of the Census: Marriage, fertility, and child 

spacing August 1959. Current Population Repo?ts, Series P20, No. 108. Washington, D. C., 1961. 

13Weetoff, C. F., Mishler, E. G., and Kelly, E. L.: Preferences in size of family and eventual fertility gwenty years 

after. Am. J. Sociol. 62(5):491-497, Mar. 1957. 

14Goldberg, D., Sharp, H., and Freedman, R.: The stability 

and reliability of expected family size data. hlitbank Mcm. 

Fund Quart. 37(4): 369-385, Oct. 1959. 

15Westoff, C. F., Potter, R. G., and Sagi, P. C.: Op. rif. 

ch. 7. 

16 Campbell, A. A., Whelphn, p. K., and Tomasson, R. F.: 

Op. cit. 

17 Freedman, R., Whelpton, P. K., and Campbell, A. A.: 

Op. cit. 

24 
APPENDIX 

DEFINITIONS 

The terms listed below are used in the present report. 

The list is divided into two broad categories, fertility 

concepts and fertility measures. Under concepts are included very general terms describing various aspects 

of fertility. The terms listed under measures are divided into two groups, measures of period fertility and 

measures of cohort fertility. 

Fertility Concepts 

Bt%th cohort. —A group of persons born in a given 

12-month period. In this report the birth cohort of 

1930, for example, refers to women born in the period 

July 1, 1929, to June 30, 1930, 

CohoYt.-In this report synonymous with birth 

cohort. See also marriage cohort. 

Coho)’t fe~tility. —An approach to the study of fertility thfit concentrates attention on the childbearing 

history of a group of women as they live through the 

reproductive years of life. The average number of 

children ever born by a given age (for a birth cohort) 

or by a given duration of marriage (for a marriage 

cohort). 

Cohort fertility Yates.— Rates that relate to births 

that occur to a specified group of women born or married in the same year. 

Fectmdity. —The physiological capacity to participate in conception or reproduction. 

Fertility. —The number of children actually born 

to a woman, couple, or group (in contrast to fecundity). 

Marriage cohort. —A group of persons married 

during a. given year. 

PaYity. —The number of children a woman has 

borne, For example, a zero-parity woman has borne no 

children, a one-parity woman has lmrne one child, and 

so on. 

Pe~iodfe~tility. — Any measure of fertility relating 

to births in a given segment of time, most commonly a 

single calendar year or 5-year period. 

Period rates. –Rates that relate to births which 

occur in a specified time interval (usually a calendar 

year) as distinguished from cohort rates. 

Sfiacing of Mtlzs. —Interval between marriage and 

first birth and between births of successive order. 

OF TERMS 

Timing of births. —The time of birth as it relates 

to the mother’s age, her duration of marriage, or the 

length of time since her preceding birth. 

Fertility Measures 

1. MEASURES OF PERIOD FERTILITY 

Age-specific birth ~ate. —The number of births occurring amually (or in a specified period) per 1,000 

women of specific age (usually in terms of 5-year age 

group). 

Birth rate. —Synonymous with crude birth rate. 

Gude bi~th rate.,—The number of births occurring 

in 1 year per 1,000 average or midyear population within a given area or population group. The rate is crude 

in that it relates to the total population without regard 

to age and sex. 

FeYtility rate. —A general term relating to any 

measure of ‘the reproductive performance of women or 

men of reproductive age. (Sometimes used as a brief 

term for general fertility rate.) 

FeYtiWy ratio. —The number of children under 

years of age per 1,000 women of childbearing age 

(usually 15-49 years). Also called child-woman ratio. 

General fe?’tility Yate. —The number of births occurring annually per 1,000 women of childbearing ages 

(usually 15-44 years or 15-49 years). 

GYOSS reproduction rate. —The average number of 

daughters that a hypothetical cohort of females starting 

life together would bear if they all survived from birth 

to the end of the childbearing period and if they experienced a given set of age-specific fertility rates. 

Usually this measure is computed from fertility rates 

observed in a single calendar year. It is often interpreted as showing the extent to which the generation 

of daughters would replace the preceding generation of 

females if fertility remained constant at a given level 

and if there were no deaths. 

illegitimacy ~ate.—The number of illegitimate 

births per 1,000 unmarried women of specified age 

(usually 15-19 years, 20-24 years, 15-44 years or 15-

49 years). 

25 

5 
Illegitimacy ?’atio.-The nufiber of illegitimate 

births per 1,000 live births. 

kt~imsic bivth n.zte.-The crude birth rate that 

would eventually result if a population were to experience 

given sets of age-specific mortality and fertility rates 

over a long period of time. Under these hypothetical 

conditions the age distribution of the population would 

eventually become stable, that is, the percent distribution of the population by age and sex would become 

constant. The crude birth and death ratea would also 

become constant because the same age-specific rates 

would be applied to a stable age distribution year after 

year. The intrinsic birth and death rates are often interpreted as showing the potential effects on population growth of given sets of mortality and fertility 

rates. These rates are usually computed from mortality and fertility rates observed in a given calendar 

year. 

Marital fertility Yate. —The number of births per 

married woman (or a given number of women) during 

a specified period of time. This may or may not be 

specific with reference to age of woman or duration of 

marriage. 

Net reproduction rate. —The average number of 

daughters that a hypothetical cohort of females starting 

26 

life together would bear if they experienced given sets 

of age-specific mortality and fertility rates. usu;Illy 

this measure is computed from mortality and fertility 

rates observed in a single calendar year. It is often 

interpreted as showing the extent to which a generation of daughters would replace the preceding gener ­

ation of females if mortality and fertility remained 

constant at stated levels. 

2. MEASURES OF COHORT FERTILITY 

Cumulative birth rate. —The number of children 

ever born per .1,000 women, or married women, (If 

specific age. This indicates the total past fertility c,f 

women up to a given age. 

Completed birth rate .—The cumulative birth rate 

by the end of the childbearing period (usually ages 4.5-

49 years). 

Completed fertility, completed fertility ~atc, ]Im 1 

biyth Yate, or average family size. —Synonymous with 

completed birth rate. 

Cumulative marrz”age ~ate. —The number, of firt t 

marriages occurring by a given age per 1,000 women 

in a cohort who live to that age. 

* U. S. GOVERNMENT PRINTING OFFICE : 1965 0-783-8,17 
OUTLINE OF REPORT SERIES FOR VITAL AND HEALTH STATISTICS 

Public Health Service Publication No. 1000 

Series 1. 

Sevies 2, 

Series 3. 

Series 4. 

Series 10. 

Series 11. 

SeVies 12. 

SeTies 20. 

Sevies 21. 

Series 22. 

Programs and collection procedwes. —Reports which describe the general programs of the National 

Center for Health Statistics and its offices and divisions, data collection methods used, definitions, and 

other material necessary for understanding the data. 

Reports number 1-4 

Qata evaluation and methods vesearclz. -Studies of new statistical methodology including: experimental 

tests of new survey methods, studies of vital statistics collection methods, new analytical techniques, 

objective evaluations of reliability of collected data, contributions to statistical theory. 

Reports number 1-10 

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 series. 

Reports number 1-4 

Documents and committee vepovts.— Final reports of major committees concerned with vital and health 

statistics, and documents such as recommended model vital registration laws and revised birth and 

death certificates. 

Reports number 1 and 2 

Data From the Health Interview Suvvey .—Statistics on illness, accidental injuries, disability, use of 

hospital, medical, dental, and other services, and other health-related topics, based on data collected in 

a continuing national household interview survey. 

Reports number I -22 

Data From the Health Examination Survey .—Statistics based on the direct examination, testing, and 

measurement of national samples of the population, including the medically defined prevalence of specific diseases, and distributions of the population with respect to various physical and physiological 

measurements. 

Reports number I-10 

Data From the Health Records Suvvey. —Statistics from records of hospital discharges and statistics 

relating to the health characteristics of persons in institutions, and on hospital, medical, nursing, and 

personal care received, based on national samples of establishments providing these services and 

samples of the residents or patients. 

Reports number 1 and 2 

Data on wtortaJity. -Various statistics on mortality other than as included in annual or monthly reportsspecial analyses by cause of death, age, and other demographic variables, also geographic and time 

series analyses. 

No reports to date 

Data on natality, mawiage, and divoyce. —Various statistics on natality, marriage, and divorce other 

than as included in annual or monthly reports— special analyses by demographic variables, also geographic and time series analyses, studies of fertility. 

Reports number 1-6 

Data From the National Natality ad Mortality Surveys. —Statistics on characteristics of births and 

deaths not available from the vital records, based on sample surveys stemming from these records, 

including such topics as mortality by socioeconomic class, medical experience in the last year of life, 

characteristics of pregnancy, etc. 

Reports number 1 

IJor a list of titles of reports published in these series, write to:	 National Center for Health Statistics 

U.S. Public Health Service 

Washington, D.C. 20201