MEASURE DHS+ assists countries worldwide in the collection and use of data to monitor and evaluate

population, health, and nutrition programs. Funded by the U.S. Agency for International Development (USAID),

MEASURE DHS+ is implemented by ORC Macro in Calverton, Maryland.

The main objectives of the MEASURE DHS+ project are: 

1) to provide decisionmakers in survey countries with information useful for informed policy choices, 

2) to expand the international population and health database, 

3) to advance survey methodology, and 

4) to develop in participating countries the skills and resources necessary to conduct high-quality demographic

and health surveys.

Information about the MEASURE DHS+ project or the status of MEASURE DHS+ surveys is available on the

Internet at http://www.measuredhs.com or by contacting: 

ORC Macro

11785 Beltsville Drive, 

Suite 300

Calverton, MD 20705 USA

Telephone: 301-572-0200

Fax: 301-572-0999

E-mail: reports@macroint.com
DHS Analytical Studies No. 2

Gap between Preferred and Actual 

Birth Intervals in Sub-Saharan Africa:

Implications for Fertility and Child Health

Hantamalala Rafalimanana

Charles F. Westoff

March 2001

ORC Macro

Calverton, Maryland USA
Hantamalala Rafalimanana is Population Affairs Officer, Population Division, United

Nations, Two United Nations Plaza, New York, NY 10017. E-mail:

rafalimanana@un.org. Charles F. Westoff is Professor Emeritus and Senior Research

Demographer, Office of Population Research (OPR), Princeton University. At the time

this research was conducted, the first author was a Mellon Fellow at OPR.

Recommended citation:

Rafalimanana, Hantamalala and Charles F. Westoff. 2001. Gap between Preferred

and Actual Birth Intervals in Sub-Saharan Africa: Implications for Fertility and Child

Health. DHS Analytical Studies No. 2. Calverton, Maryland: ORC Macro.
iii

Contents

Page

Preface .................................................... v

Acknowledgments .......................................... vi

Executive Summary ......................................... vii

1 Introduction and Background ............................. 1

2 Data and Methodology .................................. 2

Data Source ........................................ 2

Measurement Issues ................................. 3

Methods .......................................... 4

Selection of the Actual Birth Interval (ABI) 

 And Computation of Its Length ........................ 4

Selection of the Preferred Birth Interval 

 And Computation of Its Length ........................ 5

Measurement of the Implications of Birth

 Spacing Preferences ................................ 5

Model Definition for the Analysis of the

 Covariates of the PBI ............................... 5

3 Results .............................................. 7

Differences between Actual and Preferred 

 Length of Birth Intervals ............................. 7

Child Mortality Implications ........................... 9

Child Nutritional Status Implications .................... 11

Fertility Implications ................................ 12

Covariates of Preferred Birth Interval Length ............. 14

Trends in Preferred Birth Interval Length ................ 14

Trends in Actual Birth Interval Length .................. 16

4 Conclusions and Discussion ............................. 17

Policy and Program Significance ....................... 18

References ................................................ 20
iv
v

Preface

One of the most significant contributions of the MEASURE DHS+ program is the creation of an internationally comparable body of data on the

demographic and health characteristics of populations in developing countries.

The DHS Analytical Studies series and the DHS Comparative Reports series

examine these data, focusing on specific topics. The principal objectives of

both series are: to provide information for policy formulation at the international level, and to examine individual country results in an international

context. Whereas Comparative Reports are primarily descriptive, Analytical

Studies take a more analytical approach. 

The Analytical Studies series comprises in-depth, focused studies on a

variety of substantive topics. The studies are based on a variable number of

data sets, depending on the topic under study. A range of methodologies is

used, including multivariate statistical techniques. The topics covered are

selected by MEASURE DHS+ staff in conjunction with the MEASURE DHS+

Scientific Advisory Committee and USAID.

It is anticipated that the Analytical Studies will enhance the

understanding of significant issues in the fields of international population and

health for analysts and policymakers.

Martin Vaessen

Project Director
vi

Acknowledgments

This research was supported by a grant from the Rockefeller

Foundation and indirectly by a postdoctoral fellowship from the Andrew

Mellon Foundation. The authors would like to thank Luis Rosero-Bixby for his

comments on our approach to the measurement of preferred birth intervals,

Shea Rutstein for his comments on the draft manuscript, and Germán

Rodríguez for statistical advice. A shorter version of this report, covering

fewer countries, was published recently in Studies in Family Planning. The

opinions expressed in this report are those of the authors and do not necessarily

reflect the views of the United Nations.
vii

Executive Summary

Using Demographic and Health Surveys (DHS) data from 20 subSaharan countries, this article compares women’s actual lengths of birth

intervals to preferred lengths and assesses the implications of the difference for

selected demographic and health indicators. The results show a clear pattern.

Women prefer much longer birth intervals than they actually have in Comoros,

Ghana, Kenya, Rwanda, and Zimbabwe, compared with women in the other

15 countries studied. As a consequence, the potential effects of spacing

preferences on the level of fertility, as well as on the prevalences of short birth

intervals (less than 24 months) and child malnutrition, are greatest in the same

five countries. An explanation based on the observed sharp decline in fertility

recently experienced by these five “forerunners” is offered for this pattern.

The covariates of preferred birth interval lengths are also examined. In

general, women who know, approve of, discuss, and use family planning

prefer longer intervals than their counterparts. The educational attainment of

husbands matters more than that of female respondents in determining spacing

preferences. For nine countries that have conducted more than one survey, an

average increase of six months in the length of preferred intervals is

documented. Similarly, data from 12 countries that conducted a survey in the

mid- or late 1990s show an increase in the actual lengths of birth intervals; the

magnitude of the increase is higher in the most recent period studied (when

intervals starting in the 1980s are compared with intervals starting in the

1990s). The policy and program relevance of these results is discussed.
1

1 Introduction and Background

Perhaps the most fundamental and important population policy guideline is the premise that

individuals and couples should be enabled to realize their reproductive intentions and preferences, that

is, to have the number and spacing of children they desire. This premise conventionally translates into

the promotion of family planning and related reproductive health measures.

A considerable amount of research has now been accumulated to document the extent to which

reproductive preferences are being exceeded. Estimates of unwanted fertility have been calculated for

many countries (Adetunji, 1998; Bankole and Westoff, 1995; Westoff, 1991) and the desired number

of children have been compared with the actual number born. The general conclusion of this research

is that there is a significant amount of unwanted fertility throughout the developing world, which is

particularly evident in the middle stages of the fertility transition when women are increasingly aiming

for fewer children (Bongaarts, 1997). In sub-Saharan Africa, this fertility transition has only recently

begun. Therefore, in this part of the world, significant levels of unwanted fertility are evident only in

a few countries compared with other parts of the developing world.

However, few studies have examined the spacing component of reproductive intentions. One

study of sub-Saharan Africa revealed the widespread desire of women to have longer birth intervals

than they are currently having in the region. Between a quarter and a third of women reported that

they had recently experienced a birth sooner than they wanted (Bankole and Westoff, 1995).

This reproductive preference for spacing instead of limiting is peculiar to sub-Saharan Africa.

It raises the following important question: Do family planning program efforts, which have focused

on birth spacing rather than on birth limiting in this region, have the potential for changing the

dynamics of the region’s population? We suspect that the answer to this question is positive for two

main reasons. First, if people prefer to avoid short birth intervals, and if these aspirations are realized,

mortality and morbidity will eventually reach lower levels given the well-documented detrimental

effects of short birth intervals on the lives of women and children (e.g., National Research Council,

1989; Population Reference Bureau, 1995). Second, the desire to lengthen birth intervals could fuel

the fertility transition, initially because extending the interval between births, i.e., delaying births,

would lower the birth rate. The rate of population growth would be reduced as the length of the

generation is increased. The demographic mechanism is similar to increasing the age at marriage,

which would normally increase the age at first birth. Moreover, some of the postponed births would

never occur. 

In this study, we examine the extent to which the above hypothesis is true. More specifically,

we compare the lengths of the birth intervals that women have with the birth interval lengths they

would prefer to have. Then we assess the implications of the difference for the demography and health

of sub-Saharan Africa. The question is the same as that which has guided the study of unwanted

fertility: What would the fertility rate be if women’s desired numbers of children prevailed? We restate

the question in terms of birth spacing preferences and ask what birth intervals would result if women

had their ideal spacing preferences and what implications their “preferred” intervals would have for

fertility, child mortality, and child nutritional status. We also analyze the covariates of the preferred

lengths of birth intervals in the region. Finally, we examine the trends in the preferred and actual

lengths of birth intervals.
2

2 Data and Methodology

Data Source

Data for this study are from the Demographic and Health Surveys (DHS) carried out in subSaharan Africa. The DHS surveys are broadly comparable surveys that have been conducted since

1985 in many countries throughout the developing world, with funding mainly from the U.S. Agency

for International Development (USAID). These surveys have collected extensive information on

fertility, fertility preferences, child mortality, and maternal and child health indicators from nationally

representative samples of women of reproductive age (15-49 years old). Thus, the surveys permit a

comparative examination of birth spacing in a broad range of countries. We limit ourselves to the data

collected in the region in the 1990s (DHS-II and DHS-III rounds). For countries where more than one

DHS survey has been conducted during this decade, we use data from the most recent survey, with the

exception of the analysis of trends. This research is based on data from 20 African countries (see

Table 1 for general information regarding the data sources).

Table 1 Data sources and numbers of women, actual birth intervals (ABI), and

preferred birth intervals (PBI) analyzed, by country

_________________________________________________________________

Number 

Source Year(s) ______________________ 

Country of data of survey Women ABI PBI 

_________________________________________________________________

West and Middle Africa

Benin DHS-III 1996 3,183 7,320 4,579

Burkina Faso DHS-II 1992-93 3,735 8,335 7,190

Cameroon DHS-II 1991 1,812 4,287 3,694

Central African Rep. DHS-III 1994-95 2,522 5,832 3,652

Côte d’Ivoire DHS-III 1994 2,936 5,835 4,678

Ghana DHS-III 1993 2,358 5,130 2,976

Mali DHS-III 1995-96 5,922 14,348 9,558

Niger DHS-II 1992 3,801 9,448 8,918

Nigeria DHS-II 1990 4,666 10,982 9,615

Senegal DHS-III 1997 4,372 10,171 8,276

East and Southern Africa

Comoros DHS-III 1996 1,079 2,624 1,384

Kenya DHS-III 1998 3,142 7,103 3,568

Madagascar DHS-III 1997 2,991 7,160 3,945

Malawi DHS-II 1992 2,446 5,842 4,326

Namibia DHS-II 1992 1,511 3,449 2,824

Rwanda DHS-II 1992 2,996 7,177 4,752

Tanzania DHS-III 1996 3,792 8,592 6,851

Uganda DHS-III 1995 3,640 8,818 6,117

Zambia DHS-III 1996-97 3,655 8,592 7,228

Zimbabwe DHS-III 1994 2,529 5,275 2,992

_________________________________________________________________
3

Measurement Issues

The measurement of birth interval preferences is as challenging as the measurement of

unintended fertility and raises many of the same methodological questions (Rosero-Bixby, 1998). The

subject of spacing preferences is represented in the DHS core questionnaire with three approaches,

each with certain strengths and weaknesses:

1. Best length for a birth interval. All respondents were asked the following question: “What do

you think is the best number of months or years between the birth of one child and the birth of the

next child?” Answers to this question provide a first approximation of the length of the preferred

birth interval (PBI) (Bankole and Westoff, 1995). The advantages of this approach are that it is

direct and explicit; it focuses exactly on the topic of interest; and it was asked of all women, not

just those who wanted another child. One disadvantage, however, is that it has the abstract quality

of an ideal, which may or may not be relevant to the individual’s situation. In this way, it is

comparable to the standard question about the ideal number of children. Another drawback is that

the responses to the question are stereotyped (most were reported in full years) and concentrated

on two, three, and four years. In Niger, for example, 49 percent of responses are in the two-year

category and 41 percent are in the three-year category (Bankole and Westoff, 1995). This

distribution does not mean that the responses are meaningless, but they are less useful for purposes

of further analysis.

2. Preferred length for the next birth interval. Women who said that they wanted another child and

who were not pregnant at the interview were asked the following question: “How long would you

like to wait from now before the birth of another child?” In this question, “now” refers to the date

of the interview. Women who were in the same category but pregnant at the interview were asked

the following: “How long would you like to wait after the birth of the child you are expecting

before the birth of another child?” Answers to these questions measure the preferred length of the

next birth interval, which can be considered a second estimate of the PBI (Bankole and Westoff,

1995). For a nonpregnant woman, the preferred length of the next interval is defined as the sum

of the observed open interval (the months since the last birth) and the additional preferred waiting

time. For a pregnant woman, it is derived from her answer to the question about the waiting period

that she desires between her next two births. This approach has the advantage of focusing on the

woman’s personal perspective rather than on an ideal, and it also generates distributions that

typically range across six 12-month intervals. However, the resulting PBI estimate is probably

biased by selection effects. First, it is based only on the responses of women who want more

children, who may on average desire shorter times between births. Second, it reflects the open

birth interval, which tends to be longer than closed birth intervals. Another weakness of this

approach, as well as of the following approach, is that the structure of the questions does not permit

negative responses. For example, subfecund women may feel that they have already waited longer

than they wanted, but the only response permitted to them is of the type “soon” or “now,” which

is classified as zero desired waiting time. Whereas the “best length of birth interval” measure is

comparable to the “ideal number of children” variable, the “preferred length of the next interval”

is analogous to whether women want more or no more children (Bongaarts, 1992).

3. Preferred lengths for the past (closed) birth intervals. Women who experienced a birth in recent

years were asked the following question: “At the time you became pregnant with (name), did you

want to become pregnant then, did you want to wait until later, or did you want no more children

at all?” This information was obtained for all births occurring in the five- or three-year period

preceding the survey, and previous studies have focused on women’s reports of the planning status

of their last birth to get a third estimate of the PBI. Bankole and Westoff (1995) proposed the
4

actual length of the last closed birth interval for women who reported that they had wanted their

last birth then, that is, at the time it occurred, as a measure of PBI. Rosero-Bixby (1998) added the

information provided by women who had wanted their last birth later to that provided by the group

of women who had wanted their last birth then to derive an estimate for most women. Women who

did not want more children are excluded. These two measures are attractive and empirically based.

They have some weaknesses, however, including that (1) they are postfactum measures and are

therefore subject to rationalization bias; (2) they are based on closed birth intervals and are

therefore subject to selection bias; and (3) they represent only women who have had a birth in the

past five or three years and exclude the preferences of those whose last birth was unwanted. This

approach is analogous to the “wanted” and “unwanted” fertility rate calculations and shares some

of the same types of problems (Bongaarts, 1990; Kulkarni and Choe, 1998).

All four measures yield plausible estimates of the length of the PBI. However, besides their

drawbacks already mentioned, the estimates have the further disadvantage of not using all the available

information collected in the DHS surveys. Each of the previous estimates is based on only one birth

interval per woman even though estimates for more than one birth interval can be derived for many

women. In this study, we propose a composite measure for the PBI, one that is based on all birth

intervals (open and closed) starting in a prescribed period and for which a PBI length can be computed.

This measure (whose method of computation is described in the next section) is more satisfactory for

two reasons (1) it is based on a cohort or longitudinal analysis and is therefore free of selection effects

(Rosero-Bixby, 1998); and (2) it combines women’s spacing preferences on both their past and future

intervals and is therefore representative of preferences over a long period.

Methods

The ideal cohort approach consists of following a cohort of women who just got married or

who just gave birth and asking them, at that moment and at each subsequent interval they are about

to start, about their preferences for the interval in question. The full birth history data collected by each

DHS survey permits a retrospective simulation of this cohort approach by selecting subgroups of

women who started an interval in a predetermined period. This procedure is equivalent to selecting

all birth intervals that started in that period. As noted earlier, this cohort approach solves the selection

bias problem, but the retrospective version proposed here still allows for the possibility of recall or

rationalization biases (Rosero-Bixby, 1998).

Selection of the Actual Birth Interval (ABI) and Computation of Its Length

In this paper, we examine birth intervals that (1) started during the ten-year period preceding

the survey and (2) ended within the five-year or three-year period (depending on the survey round)

before the survey or were expected to end after the survey. The choice of the ten-year “starting”

window was a compromise between including as many birth intervals as possible and minimizing the

possibility of recall errors associated with more distant events. The choice of the five- or three-year

“ending” window was dictated by the fact that retrospective fertility preferences were asked about only

for children who were born during this period or who were expected to be born after the survey. Only

birth intervals after the first birth are included because of the problems of dating the beginning of the

first interval. There are problems with the accuracy of reporting dates of marriage or the beginning

of informal unions, and these dates may be influenced by the pregnancy itself. Also, only birth

intervals of currently married women are included to control for any differential preference by marital

status. Because the birth intervals that are analyzed include both open (i.e., censored cases) and closed

intervals (i.e., failures), we estimate the distribution of the actual length of these birth intervals with life

table techniques.
5

Selection of the Preferred Birth Interval and Computation of Its Length

The algorithm used here includes only those birth intervals that ended with or were expected

to end with a wanted birth. For closed intervals, if the birth closing the interval was wanted then, the

PBI is equal to the ABI; if the birth closing the interval was wanted later, the PBI equals the ABI plus

the additional time the woman reports that she would have wanted to wait. For open intervals, if the

woman wanted a birth now or soon, the PBI equals the ABI; if she wanted a birth later, the PBI equals

the ABI plus the desired waiting time till the next birth. Table 1 shows the numbers of actual and

preferred birth intervals included for each country.

Measurement of the Implications of Birth Spacing Preferences

We analyze the implications of the realization of birth spacing preferences for three

demographic and health measures. They are (1) child mortality, measured by the probabilities of dying

from birth to age 1 month (neonatal mortality risks), to age 1 (infant mortality risks), and to age 5

(under-five mortality risks); (2) child nutritional status, measured by indicators of undernourishment

according to three anthropometric indices (height-for-age, weight-for-age, and weight-for-height); and

(3) fertility, measured by the total fertility rate (TFR). The procedure followed for assessing the effect

of the realization of birth spacing preferences on child survival is to calculate the actual mortality rates

for all births occurring in the ten years before the interview and then to relate these rates to the length

of the preceding birth interval. Using this standard, we then adjust the distributions of the interval

lengths to those preferred by the mothers and recalculate the expected mortality rates. The procedure

followed for assessing the child nutritional status implications of preferred birth intervals is to calculate

the percentages of children who are stunted, wasted, and underweight among all children whose

height, weight, and age could be collected at the interview (these children are aged 0 to 59 months in

the DHS-II data and 0 to 35 months in the DHS-III data). We classify these prevalences by length of

the preceding birth interval. Using the resulting distributions as standards, we then adjust the

distributions of the interval lengths to those preferred by the mothers and recalculate the expected

malnutrition prevalences. Note that our implicit assumption here is that the malnutrition rates of

children born in the ten-year period preceding the survey are the same as the malnutrition rates of

surviving children born three or five years before the survey.

Model Definition for the Analysis of the Covariates of the PBI

The potential effects of the realization of birth spacing preferences will be more useful for

policy purposes if we know the characteristics of women who prefer intervals of different lengths. In

this analysis, we fit a multiple linear regression model to individual birth interval data to examine the

covariates of the PBI. The dependent variable is the estimated length of the preferred birth interval

expressed in months. To account for the clustered nature of the data, we compute robust standard

errors for the regression parameters using Huber’s method (StataCorp, 1997). The independent

variables include the survival status of the child that opens the birth interval, the length (in months) of

the previous birth interval, the woman’s age (in years) at the interview (simple and squared), her

number of surviving children, her desire for more children, her knowledge of a method of

contraception, her use of a method of contraception, her approval of family planning, her discussion

of family size with her husband, the number of mass media she is exposed to every week, her

education, her type of residence and region, and her husband’s education. We include the actual

length of the birth interval as a control because the PBI is constructed from it. We also control for

whether the interval is open (reference category) or closed. The survival status of the child opening

the interval indicates whether that child was still alive at the conception of the next child (reference
6

category). The desire for more children indicates whether or not the woman is infecund or sterilized

or wants no more children (reference category). Knowledge of a method of contraception is a score

variable whose values are 0 when the woman does not know any method, 1 when the woman knows

at most a folk method (e.g., strings and herbs), 2 when the woman knows at most a traditional method

(e.g., periodic abstinence and withdrawal), and 3 when the woman knows at least a modern method.

Ever use of a method of contraception is also a score variable varying from 0 for women who have

never used any method to 3 for those who have ever used a modern method. Approval of family

planning indicates whether the woman does not approve of family planning (reference category) or

approves. Discussion of desired family size indicates whether the woman has ever discussed it with

her husband. The woman’s and her husband’s educational levels are score variables taking the values

0 if they are uneducated or illiterate, 1 if they have a primary level education, and 2 if they have a

secondary or higher education level. The type of residence indicates whether the woman lives in an

urban (reference category) or in a rural area.
7

3 Results

Differences between Actual and Preferred Length of Birth Intervals

In the 20 sub-Saharan countries included in this study, the median length of actual birth

intervals is 2.8 years (33.7 months) on average compared with almost 3.5 years (39.9 months) if

preferences prevailed. Figure 1 shows that the median preferred length is at least 2.5 years in every

country and as long as four years in five countries (Comoros, Ghana, Kenya, Rwanda, and Zimbabwe).

Regional differences can be observed, with women in East and Southern Africa preferring longer birth

intervals than those in West and Middle Africa. Because the actual median length does not vary across

these two subregions, these differences imply a greater potential increase in length of birth interval in

the first subregion. On average, birth intervals would increase by 24 percent in East and Southern

Africa if women realized their preferences; in West and Middle Africa, they would be 13 percent

longer, as shown in Table 2. The greatest differences between actual and preferred spacing of births

are observed in the group of countries where women prefer the longest intervals. In Comoros, Ghana,

Kenya, Rwanda, and Zimbabwe, birth intervals would increase by 33 percent or more if women’s

preferences were realized. Births occur more than one year sooner than women prefer in these

countries. In the remaining 15 countries, the median PBI is three years on average, and the resulting

potential increase in birth intervals is around 11 percent.

From the point of view of the potential reduction in neonatal and infant mortality, the critical

consideration is the prevalence of short intervals, particularly intervals of less than two years. In subSaharan Africa, an average of 17 percent of actual birth intervals are “short” by this criterion. If

women’s preferences prevailed, this percentage would decline to 11 percent but would not drop to

zero, which would 

Table 2 Median lengths (in months) of actual and preferred birth intervals

in sub-Saharan Africa, Demographic and Health Surveys, 1990-1998

___________________________________________________________

Actual birth Preferred birth Percent

Country intervals intervals increase

___________________________________________________________

West and Middle Africa

Benin 34.8 38.8 11.5

Burkina Faso 35.8 40.0 11.7

Cameroon 31.5 33.5 6.3

Central African Rep. 32.2 35.9 11.5

Côte d’Ivoire 34.2 38.6 12.9

Ghana 38.9 51.6 32.6

Mali 31.9 37.0 16.0

Niger 31.0 34.1 10.0

Nigeria 31.9 32.1 0.6

Senegal 34.0 39.8 17.1

East and Southern Africa

Comoros 30.9 47.4 53.4

Kenya 34.6 48.8 41.0

Madagascar 30.9 37.3 20.7

Malawi 33.3 37.6 12.9

Namibia 34.9 35.7 2.3

Rwanda 32.7 47.3 44.6

Tanzania 34.9 39.2 12.3

Uganda 33.1 34.5 4.2

Zambia 32.0 36.0 12.5

Zimbabwe 40.0 53.4 33.5

___________________________________________________________
8

40.0

32.0

33.1

34.9

32.7

34.9

33.3

30.0

34.6

30.9

24 30 36 42 48 54 60

Zimbabwe

Zambia

Uganda

Tanzania

Rwanda

Namibia

Malawi

Madagascar

Kenya

Comoros

Actual Length Preferred Length

47.4

48.8

35.7

47.3

39.2

36.0

53.4

EAST AND SOUTHERN AFRICA

Months

37.3

37.6

34.5

34.0

31.9

31.0

31.9

38.9

34.2

32.2

31.5

35.8

34.8

2 4 3 0 3 6 4 2 4 8 5 4 6 0

Senegal

Nigeria

Niger

Mali

Ghana

Côte d'Ivoire

Central Africa

Cameroon

Burkina Faso

Benin 38.8

40.0

38.6

51.6

37.0

32.1

39.8

Figure 1 Median lengths of actual and preferred birth intervals in 

sub-Saharan Africa, Demographic and Health Surveys, 1990-1998

WEST AND MIDDLE AFRICA

Months

33.5

35.9

34.1
9

be considered ideal by many researchers in the health field. Table 3 shows that the potential reduction

in the prevalence of short intervals would be greatest in Comoros (73 percent), and Ghana, Kenya, and

Zimbabwe (almost 60 percent); it would be as much as 50 percent in Benin, Mali, and Rwanda. 

Child Mortality Implications

There are various hypotheses about why a reduction of short birth intervals should be expected

to result in lower mortality rates in the first years of life. These include the harmful effects of the early

weaning of a child when another birth follows closely; “maternal depletion syndrome,” which drains

the mother’s strength and can result in poor birth outcomes (low birth weight and prematurity) and

poorer nutrition for children; and a variety of socioeconomic pressures resulting from the additional

drain on household resources (Boerma and Bicego, 1992). Whatever the mix of reasons, there is an

unquestionably strong relationship between the length of birth intervals and the risk of child death

(Hobcraft et al., 1985; Rutstein, 1984; Sullivan et al., 1994; Bicego and Ahmad, 1996). In a recent

study of the effects of length of birth interval on infant and child mortality in 20 developing countries,

Bicego and Ahmad (p. 25) concluded that “[s]hort preceding birth intervals are associated with a 58

percent higher risk of dying before the age of five while long birth intervals are associated with 28

percent lower risk of dying, compared with intervals 24 to 47 months in length.” They further note

that the greatest effects occur during the neonatal period.

According to the results shown in Figure 2, the reduction in neonatal mortality rates that could

be expected if birth interval preferences prevailed ranges from essentially zero in Nigeria and

Zimbabwe to a high of more than 17 percent in Kenya. The average reduction is 7 percent. The

potential reductions in infant and child mortality rates are of the same magnitude (7 percent and 6

percent, respectively).

Table 3 Actual and theoretical (if preferred birth intervals prevailed)

percentages of birth intervals that are less than 24 months in sub-Saharan

Africa, Demographic and Health Surveys, 1990-1998

___________________________________________________________

If PBI Percent

Country Actual prevailed decrease

___________________________________________________________

West and Middle Africa

Benin 12.8 6.3 50.8

Burkina Faso 10.8 8.0 25.9

Cameroon 18.7 15.1 19.3

Central African Rep. 20.1 12.4 38.3

Côte d’Ivoire 11.3 8.1 28.3

Ghana 11.4 4.8 57.9

Mali 20.9 10.7 48.8

Niger 20.6 15.1 26.7

Nigeria 21.3 20.1 5.6

Senegal 13.7 8.6 37.2

East and Southern Africa

Comoros 26.9 7.4 72.5

Kenya 18.2 8.1 55.5

Madagascar 25.2 14.3 43.3

Malawi 16.7 10.2 38.9

Namibia 16.8 15.3 8.9

Rwanda 16.6 8.9 46.4

Tanzania 13.2 9.6 27.3

Uganda 24.1 14.9 38.2

Zambia 15.6 10.6 32.1

Zimbabwe 8.8 3.6 59.1

___________________________________________________________
10

6.7

0.4

13.2

11.9

6.4

9.9

4.2

9.1

0.4

6.2

10.5

8.0

3.7

7.1

4.9

6.6

2.7

9.9

11.8

5.5

7.0

3.2

6.6

4.3

4.9

5.9

5.9

10.5

5.0

0.0

0 5 1 0 1 5 2 0

Senegal

Nigeria

Niger

Mali

Ghana

Côte d'Ivoire

Central Africa

Cameroon

Burkina Faso

Benin

Figure 2 Estimated percent reductions in child mortality rates 

in sub-Saharan Africa if preferred birth intervals prevailed, 

Demographic and Health Surveys, 1990-1998

WEST AND MIDDLE AFRICA

-3.0

11.2

6.8

1.7

5.7

17.3

0.7

5.3

7.6

3.4

1.2

5.0

13.3

13.1

0.5

0.2

6.2

3.3

10.6

0.9

4.2

11.4

10.7

12.4

1.2

7.2

12.8

2.7

9.1

11.8

- 5 0 5 1 0 1 5 2 0

Zimbabwe

Zambia

Uganda

Tanzania

Rwanda

Namibia

Malawi

Madagascar

Kenya

Comoros

Neonatal mortality Infant mortality Under-five mortality

-

EAST AND SOUTHERN AFRICA

Percent reduction
11

These reductions in child mortality that would be realized if women’s stated preferences for

the lengths of birth intervals prevailed are rather modest. The main reason for this is that the expected

reduction in the proportion of birth intervals of less than 24 months are small. As noted above, these

proportions would decline from an average of 17 percent to 11 percent. If the proportion of short birth

intervals were to drop to zero and these short intervals were to increase to 24 to 47 months duration,

the expected reduction in infant mortality, for example, would be an average of 13 percent rather than

7 percent for these 20 countries. Such a reduction would largely exhaust the connection between the

birth interval and mortality.

Child Nutritional Status Implications

We have also examined the implications of preferred longer birth intervals for the prevalence

of malnutrition of children in these 20 African countries. The DHS data include anthropometric

measures for each respondent’s young child. These measures, which have been demonstrated to

provide good summaries of children’s nutritional status (World Health Organization, 1986, 1995), are

height-for-age, weight-for-height, and weight-for-age. Following the recommendations of the World

Health Organization (WHO), these measures are already standardized using the distribution of the U.S.

National Center for Health Statistics (NCHS) reference population. Three indicators of malnutrition

are commonly constructed from these measures; these are (1) an indicator of stunting, a condition

reflecting chronic malnutrition and manifested by a low height-for-age; (2) an indicator of wasting, a

condition reflecting acute or recent malnutrition and manifested by a low weight-for-height; and (3)

an indicator of underweight, a condition reflecting chronic and/or acute malnutrition and manifested

by a low weight-for-age. In this analysis, a child was classified as “stunted” if s/he was below minus

two standard deviations (-2 SD) from the reference median in terms of height-for-age, as “wasted” if

below -2 SD from the reference median in terms of weight-for-height, and “underweight” if of a low

weight-for-age by the same criterion.

Of course, the relationship between short previous birth interval and child nutrition may be due

to other common factors such as mother’s education, family income, sex of the child, and birth order,

some of which could also impinge on the association between the time since the preceding birth and

infant and child mortality. The results even without such controls, however, show little association,

except in Comoros, Ghana, Kenya, and Zimbabwe (see Table 4). In these four countries, the

realization of preferred birth intervals would, on average, reduce stunting, wasting, and underweight

by 7 percent, 10 percent, and 8 percent, respectively. In the remaining 16 countries, the expected

reduction in the prevalence of malnutrition is less than 2 percent, on average.

Fertility Implications

The implications for the fertility rate of longer birth intervals should be significant in subSaharan Africa since contraception is used mostly for spacing (Westoff and Ochoa, 1991). The

question is how much of a potential decline in fertility could be realized if women experienced their

preferred intervals between births. If we assume that the risk of childbirth is constant, the theoretical

effect on fertility is proportionate to the inverse of the increase in the length of the interval; that is:

PTFR/ATFR = 1/(PBI/ABI) > (ATFR-PTFR)/ATFR = 1 - [1/(PBI/ABI)],

where PTFR is the TFR value if preferred birth intervals were realized;

ATFR is the actual TFR;

PBI is the preferred length of birth interval;

ABI is the actual length of birth interval.
12

Because the birth intervals included in this analysis are based only on second and higher order

events, the question arises whether the imputed effects of longer intervals should be confined to that

part of the total fertility rate. The decision was reached to use the regular TFR including first births

because even if measuring the first birth interval (that is, that between marriage and first birth) is

difficult, all first births are not necessarily timed according to women’s preferences (as many premarital

conceptions and even births would seem to imply). The implicit assumption, therefore, is that the

average preferences for longer subsequent intervals would also apply to first birth intervals.

If the preferred intervals were realized, the TFR would decline by an average of 11 percent in

West and Middle Africa and by 17 percent in East and Southern Africa (see Figure 3). There is a wide

range of imputed effects. The TFR would potentially decline by one-third in Comoros, Kenya, and

Rwanda, by a one-fourth in Ghana and Zimbabwe, and by an average of 9 percent in the remaining

15 countries. The theoretical effects on fertility are considerably greater than those on infant and child

mortality. 

These fertility effects should be considered upper limits because they do not take into account

any fertility reducing factor (e.g., the use of contraception in each interval) that women might introduce

to implement their preferences for longer birth intervals. Unfortunately, such information is not

available in the DHS data.

In the future, it would be interesting to take into account the trends in contraceptive use for

limiting because the effects of spacing desires on fertility will become weaker as the number of women

using contraception for limiting increases.

Table 4 Actual and theoretical (if preferred birth intervals prevailed) percentages of malnourished children in

sub-Saharan Africa, Demographic and Health Surveys, 1990-1998

________________________________________________________________________________________

Stunted Wasted Underweight

 _____________________ _____________________ _____________________

If PBI Percent If PBI Percent If PBI Percent

Country Actual prevailed decrease Actual prevailed decrease Actual prevailed decrease

________________________________________________________________________________________

West and Middle Africa

Benin 25.5 24.8 2.7 14.5 13.9 4.4 29.3 28.5 2.8

Burkina Faso 30.3 29.4 2.8 12.1 12.4 -2.4 29.4 28.7 2.6

Cameroon 22.8 22.9 -0.7 3.3 3.3 0.1 12.7 12.7 0.4

Central African Rep. 34.0 33.1 2.7 7.7 7.6 1.1 28.8 28.2 2.0

Côte d’Ivoire 23.4 22.4 4.7 8.4 8.4 0.8 23.3 22.3 4.2

Ghana 24.9 22.0 11.8 12.7 12.2 4.1 28.2 26.5 6.1

Mali 30.3 28.8 4.9 24.2 24.2 0.2 40.8 39.6 2.8

Niger 35.5 34.8 2.1 14.5 14.4 0.6 38.7 38.1 1.5

Nigeria 40.1 40.0 0.1 8.3 8.4 0.0 32.9 32.9 0.0

Senegala u u u u u u u u u

East and Southern Africa

Comoros 34.5 33.5 2.9 8.1 7.0 13.6 26.3 24.8 5.8

Kenya 33.5 31.3 6.6 6.2 5.8 6.6 22.5 21.0 5.8

Madagascar 46.1 45.2 1.9 7.7 7.4 3.3 39.2 38.4 2.1

Malawi 45.7 45.1 1.2 4.5 4.3 3.4 24.8 24.6 0.9

Namibia 29.3 29.2 0.2 9.1 9.1 0.0 27.5 27.5 0.0

Rwanda 47.7 45.0 5.6 3.7 3.9 -6.3 29.4 28.8 2.2

Tanzania 44.0 43.2 1.7 7.2 7.3 -0.1 31.3 31.1 0.7

Uganda 35.1 34.9 0.7 5.2 5.2 0.0 23.3 23.2 0.7

Zambia 42.8 42.3 1.2 4.3 4.3 -0.1 24.4 24.3 0.2

Zimbabwe 23.0 21.7 5.5 5.2 4.5 14.0 16.1 14.4 10.6

_______________________________________________________________________________________

a

 No data on children’s height and weight were collected in the Senegal DHS-III

u = Unknown (not available)
13

25.1

11.1

4.1

11.0

30.9

2.2

11.4

10.7

29.1

34.8

0 1 0 2 0 3 0 4 0

Zimbabwe

Zambia

Uganda

Tanzania

Rwanda

Namibia

Malawi

Madagascar

Kenya

Comoros

Reduction in TFR

EAST AND SOUTHERN AFRICA

Percent

10.5

6.0

10.3

11.4

14.1

0.6

9.1

13.8

24.6

10.3

0 10 20 30 40

Senegal

Nigeria

Niger

Mali

Ghana

Côte d'Ivoire

Central Africa

Cameroon

Burkina Faso

Benin

Figure 3 Estimated percent reductions in fertility in 

sub-Saharan Africa if preferred birth intervals prevailed, 

Demographic and Health Surveys, 1990-1998

WEST AND MIDDLE AFRICA

Percent
14

Covariates of Preferred Birth Interval Length

As shown above, the realization of birth spacing preferences has a nontrivial effect on fertility,

a more modest effect on child mortality, and little effect on child malnutrition in sub-Saharan Africa.

For policy and program purposes, it is useful to know what determines the variations in birth interval

preferences. We have examined the covariates of preferred birth interval lengths by means of a

multiple linear regression model. The results are presented in Table 5 in which, for each country, the

effect of each variable is indicated by its sign and is only indicated if the effect in question is

statistically significant at the 5 percent level.

Birth intervals in which the “opening” child died before the conception of the “closing” child

have shorter preferred lengths than intervals whose opening child was alive at the conception of the

next child. Also, birth intervals that are closed have shorter preferred lengths than do open intervals.

The length of the preceding birth interval does not influence the preferred length of the actual interval.

The preferred length of birth interval has a curvilinear relation with the woman’s age: it increases with

age, but the increase tapers off among older women (usually age 40 and over). The preferred length

also increases with the number of surviving children.

The preferred length of birth interval increases with women’s knowledge and use of

contraception. Regression models in which the variables “woman knows a modern method of

contraception” and “woman has ever used a modern method of contraception” have been substituted

for the contraceptive knowledge and use variables for any traditional method show that women who

know and/or have ever used a modern method prefer much longer birth intervals than their

counterparts (regression results not shown). Women who approve of family planning and whose

husbands are educated prefer longer birth intervals than their counterparts. Birth spacing preferences

vary significantly by region of residence. This association is not shown in Table 5 because the regions

are different from country to country. 

Finally, women’s desire for more children and rural residence are negatively associated with

preferences in less than half the countries. Similarly, women’s exposure to mass media, their

educational attainment, and their having discussed family size with their husbands are positively

associated with preferences in less than half the countries.

Trends in Preferred Birth Interval Length

With an increasing number of countries in the DHS program having repeated surveys over an

average period of five years, it is possible to assess trends in the length of preferred birth intervals. An

earlier examination (Bankole and Westoff, 1995) of this question was only able to include four subSaharan countries; there are now five more countries with repeat surveys.

The measure selected to evaluate this trend is the preferred length of the next birth interval.

We compare its medians for the earliest and the latest surveys (Kenya and Senegal had three surveys

over approximately a decade). On average, five years elapsed between surveys for the other seven

countries.

The length of the preferred next birth interval has increased in all nine countries with an

average increase of six months (see Table 6). The increase has been partitioned into two components:

the length of the open interval (the duration since last birth) and the additional time women would

prefer to wait for the next birth. With one exception (Zambia), the increase in the additional waiting

time is the major component of the increase in the overall preference. On average, this component

increased by five months while the open interval increased by only one month. One way of

interpreting the difference in these two components is that the behavioral response reflected in the

length of the open interval is changing less rapidly than the attitudinal dimension. The three countries

that show the greatest increases in the length of the open interval (Ghana, Kenya, and Zimbabwe) have

experienced the greatest increases in contraceptive use.
15

Table 5 Correlates of preferred birth intervals in sub-Saharan Africa (linear regressions), Demographic and Health Surveys, 1990-

1998

_________________________________________________________________________________________________

Effect 

______________________________________________

Variable BE BF CM CA CI GH ML NI NG SN

___________________________________________________________________________________________________

West and Middle Africa

Birth interval characteristics

Actual length + + + + + + + + + +

Closed interval - - - - - - - - - -

Child opening the interval died before conception of next child - - - - - - - - - -

Length of previous interval - - +

Woman’s demographic characteristics

Age + + + + + + + + + +

Number of surviving children + + + + + + + + + +

Woman’s knowledge and use of family planning

Level of knowledge of contraceptive methods + + + + + + + +

Level of ever use of contraceptive methods + + + + + + + +

Approval of family planning + + + + + + + + + +

Woman’s fertility preferences

Desire for more children - - - -

Discussion of desired family size with husband + + + - +

Woman’s socioeconomic status

Number of mass media she is exposed to every week + +

Educational level + + + + 

Rural residence - -

Husband’s educational level + + + + + + + 

_________________________________________________________________________________________________

Effect 

______________________________________________

Variable CO KE MD MW NM RW TZ UG ZM ZW

___________________________________________________________________________________________________

East and Southern Africa

Birth interval characteristics

Actual length + + + + + + + + + +

Closed interval - - - - - - - - - -

Child opening the interval died before conception of next child - - - - - - - - - -

Length of previous interval +

Woman’s demographic characteristics

Age + + + + + + + + + +

Number of surviving children + + + + + + + + +

Woman’s knowledge and use of family planning

Level of knowledge of contraceptive methods + + + + + + + +

Level of ever use of contraceptive methods + + + + + + + + + +

Approval of family planning + + + + + + + + +

Woman’s fertility preferences

Desire for more children - - - -

Discussion of desired family size with husband + + - + + +

Woman’s socioeconomic status

Number of mass media she is exposed to every week + + +

Educational level + - + + +

Rural residence - - - -

Husband’s educational level + + +

________________________________________________________________________________________________

BE = Benin; BF = Burkina Faso; CM = Cameroon; CA = Central African Republic; CI = Côte d’Ivoire; GH = Ghana; ML = Mali; 

NI = Niger; NG = Nigeria; SN = Senegal; CO = Comoros; KE = Kenya; MD = Madagascar; MW = Malawi; NM = Namibia; 

RW = Rwanda; TZ = Tanzania; UG = Uganda; ZM = Zambia; ZW = Zimbabwe.
16

Trends in Actual Birth Interval Length

Using the surveys carried out in the mid- and late 1990s, we also examine trends in the actual

length of birth intervals. We do not include surveys conducted in the early 1990s to avoid early

censoring of the birth intervals that start in the late 1980s and the early 1990s. Table 7, which contains

the results for 12 countries show that birth intervals have been increasing over time, especially from

the 1980s to the 1990s. The largest increases are observed in Benin, Côte d’Ivoire, Kenya, Senegal,

and Zimbabwe.

Table 6 Trends in (median) preferred lengths of next interval (in months) in sub-Saharan Africa, Demographic

and Health Surveys, 1986-1998

__________________________________________________________________________________________

Year(s) of survey Total Open interval Additional waiting time

_____________ __________________ __________________ _________________

Country t1 t2 t1 t2 difference t1 t2 difference t1 t2 difference

__________________________________________________________________________________________

Ghana 1988 1993-94 49.0 56.5 7.5 15.1 17.6 2.5 33.9 38.9 5.0

Kenya 1988-89 1998 45.4 52.1 6.7 13.7 15.7 2.0 31.7 36.4 4.7

Madagascar 1992 1997 41.2 46.4 5.2 12.9 13.0 0.1 28.3 33.4 5.1

Mali 1987 1995-96 33.5 41.1 7.6 11.8 12.8 1.0 21.7 28.3 6.6

Senegal 1986 1997 35.1 44.3 9.2 13.9 14.3 0.4 21.2 30.0 8.8

Tanzania 1991-92 1996 41.8 46.0 4.2 14.3 14.8 0.5 27.5 31.2 3.7

Uganda 1988-89 1995 30.7 38.3 7.6 11.8 12.2 0.5 18.9 26.1 7.2

Zambia 1992 1996-97 37.6 38.5 0.9 12.3 13.2 0.9 25.3 25.3 0.0

Zimbabwe 1988-89 1994 49.7 57.5 7.6 16.4 18.4 2.0 33.1 38.9 5.8

Table 7 Trends in (median) actual length of birth intervals (in months)

in sub-Saharan Africa, Demographic and Health Surveys, late 1990s.

_______________________________________________________

 Birth intervals

 starting in the:

Year(s) of ___________________

Country survey 1970s 1980s 1990s

_______________________________________________________

Benin 1996 31.2 31.8 35.5

Central African Republic 1994-95 29.5 30.8 32.9

Comoros 1996 25.2 26.7 30.9

Côte d’Ivoire 1994 29.7 30.9 35.9

Kenya 1998 27.6 29.3 34.6

Madagascar 1997 25.8 28.7 30.2

Mali 1995-96 26.9 27.8 32.6

Senegal 1997 29.6 30.2 34.3

Tanzania 1996 29.5 32.7 35.2

Uganda 1995 27.3 28.3 29.5

Zambia 1996-97 28.4 30.8 32.2

Zimbabwe 1994 30.4 35.0 40.5

_______________________________________________________
17

4 Conclusions and Discussion

The results of this analysis of birth spacing preferences in sub-Saharan Africa show that women

in Comoros, Ghana, Kenya, Rwanda, and Zimbabwe prefer much longer birth intervals than those they

actually have compared with women in the other 15 countries studied. If women’s spacing preferences

were realized, the level of fertility (and to lesser extents the levels of child mortality and malnutrition)

in these five countries would be significantly reduced, unlike that of the remaining 15 countries. Using

as a reference the TFR values published by the Population Reference Bureau (1998), we find that the

hypothetical declines in fertility would translate into 2 children fewer per woman in Comoros and

Rwanda, 1.5 fewer in Ghana and Kenya, 1 child fewer in Zimbabwe, and 0.5 fewer in the remaining

countries, on average. The implications of spacing preferences for child survival are more modest, but

not insignificant: on average, a 7 percent decrease in neonatal and infant mortality risks and a 6 percent

decrease in under-five mortality risks are observed in the 20 countries. These potential reductions in

child mortality are in line with the 10 percent or lower effects of most child survival interventions. The

implications for children’s nutritional status are small (less than 2 percent decrease in malnutrition rates,

on average) except in Comoros, Ghana, Kenya, and Zimbabwe, where the realization of preferred birth

intervals would, on average, reduce child stunting, wasting, and underweight rates by 7 percent, 10

percent, and 8 percent, respectively.

These results indicate that among the sub-Saharan countries studied, birth spacing preferences

have potential demographic and health implications in Comoros, Ghana, Kenya, Rwanda, and

Zimbabwe, but not in the other 15 countries, because women in the first five countries prefer much

longer birth intervals than those they experience compared with women in the remaining countries.

What might account for this finding? The major characteristic shared by these five countries is the

sharp decline in fertility that they have recently experienced, declines which have been associated with

significant increases in the use of contraception. In Kenya and Zimbabwe, where the DHS data have

confirmed that the fertility transition effectively began in the late 1980s, the TFR declined by 20

percent and 22 percent, respectively, during the six-year period preceding their latest DHS (National

Council for Population and Development et al., 1994; Central Statistical Office and Macro International

Inc., 1995). Similar declines in fertility have been recorded in Comoros, Ghana, and Rwanda. For

example, the TFR declined by 20 percent during the five-year period preceding the 1996 DHS in

Comoros (Mondoha et al., 1997), and by 27 percent during the nine-year period preceding the 1992

DHS in Rwanda (Barrère et al., 1994). It could be that in these environments of rapidly falling fertility,

women and couples are more aware that they can control the timing of their births to achieve smaller

families. Because of this greater awareness, they may be more likely to exert such control and

therefore more likely to react negatively when a birth occurs sooner than they would have liked,

particularly if the birth occurs shortly after the previous one. Consequently, they may be more likely

to report that a birth was mistimed in surveys.

Although this work establishes the existence of a gap between preferred and actual birth

intervals in sub-Saharan Africa, the conclusions that are drawn are limited by the validity of the

measure of the preferred birth interval. Several biases, some of which were enumerated at the

beginning of this report, might affect our estimated PBI. First, rationalization bias is a concern because

our estimation is based partly on postfactum measures. However, experimental studies conducted in

Latin America have shown that questions about preferences of the type asked by DHS surveys

minimize this problem by emphasizing the respondent’s feeling at the time of each conception

(Goldman et al. 1989; Westoff et al. 1990). A second concern is that the DHS questionnaire does not

allow respondents to give negative responses regarding spacing preferences so that women who might

have preferred shorter intervals than what they actually had were, in a sense, “forced” to report that

they were satisfied with their interval lengths. Therefore, the estimated PBIs may be upwardly biased.
18

We suspect that this problem is more likely to affect long birth intervals, that is, those longer than four

or five years. Also, the problem may be more important in countries with a high prevalence of

secondary infertility, where many women have to wait much longer than they want to before getting

pregnant. The magnitude of this bias can be assessed in the future by conducting a sensitivity analysis

in which a certain proportion (for example, one-third or one-half) of birth intervals that are longer than

48 or 60 months and that women report as having been wanted then is assumed to have in fact been

wanted some time earlier (for example, 3, 6, or 12 months). In the 20 countries examined in this study,

the proportion of birth intervals longer than 48 months that were reported as being wanted then varies

from 7 to 11 percent. For birth intervals longer than 60 months, the corresponding proportion varies

from 3 to 5 percent. These percentages seem rather low to substantially alter our conclusions. A final

concern is the exclusion of birth intervals that started in the period five (or three) to ten years before

the survey and ended in the same period. The exclusion, which was performed because no information

on spacing preferences was collected for such birth intervals, may have led to a selection of longer

intervals. A way of addressing this potential problem is to restrict the window of analysis to the fiveyear period before the survey since all intervals included in that window have complete information.

By doing so, we find that in the 20 countries, the median lengths of actual and preferred birth intervals

are on average 33.4 months and 39.0 months, respectively. On average, the corresponding potential

increase in birth interval length is 24 percent in East and Southern Africa and 12 percent in West and

Middle Africa. These results do not differ greatly from our previous findings; thus, the conclusions

should not be too sensitive to the choice of the window of analysis.

The failure to control for the strong association between birth interval length and birth order

must also be acknowledged. Lower order births tend to have shorter birth intervals, and it has been

shown that women tend to report as mistimed those births that are the result of shorter birth intervals

(Adetunji, 1998; Montgomery et al., 1997). To check whether the overall gap that exists between

actual and preferred birth intervals persists at each birth order, we computed the percentage increase

in interval length if preferences were realized for intervals starting with first births, second births, and

third or higher order births, respectively. The results are shown in Table 2. Before commenting on

them, we report that on average, the median lengths of actual following birth intervals are 31.7 months,

32.6 months, and 34.3 months for first births, second births, and third and higher order births,

respectively. The median lengths of preferred birth intervals are 38.3 months, 40.3 months, and 40.9

months, on average, for each category of birth interval. These results confirm that lower order births

precede shorter intervals. The results shown in Table 2 reveal that the gap between actual and

preferred birth intervals is generally greater for intervals starting with lower order births (first or

second) than for intervals starting with higher order births. Thus, the magnitude of the gap depends

on parity, and this relationship helps to explain why the gap is greater in countries with lower fertility

such as Comoros, Ghana, Kenya, and Zimbabwe. In the future, it would be interesting to examine

whether the implications of the gap between actual and preferred birth intervals for fertility and child

health and survival also vary by birth order. Such an examination would certainly further illuminate

the findings reported here.

Policy and Program Significance

Given the great emphasis on the promotion of family planning for purposes of birth spacing

in the region, the results of this research are directly relevant to the public health and population policy

rationales of government programs and international donor activities. 

At the program level, it is useful to know how many women in the different populations

actually prefer short intervals. Our estimate is that an average of 11 percent prefer their birth intervals

to be shorter than 24 months. In the 20 countries included in this analysis, an average of 50 percent
19

(29 percent in the group of five “forerunners” and 57 percent in the remaining 15 countries) of

currently married women whose last closed birth interval was shorter than 24 months reported that birth

to have been wanted then, not later. If this is at all typical, there is something of a health education

challenge. The point is not to demonstrate that short intervals have health implications but rather that

short intervals are not preferred by most women, although some significant fraction continue to want

such intervals. Thus, the dual aim should be to persuade some women to prefer longer birth intervals

and to enable others who already prefer such intervals to achieve that objective.

Evidence has been found (Greene, 1998) that contraception as currently used for spacing births

in sub-Saharan Africa has only a limited effect on the length of birth intervals, increasing the average

interval by only a few months. There are many methodological problems with this observation

including self-selection bias and the substitution of imperfect methods for postpartum protection, but

the observation of little effect is unsettling and, if generalizable to more countries, should be on the

agenda of program designers.

Related to this finding is the broader general question of how great of an effect on fertility the

use of contraception for spacing versus the use of contraception for limiting has in sub-Saharan Africa.

Examining this question involves estimating how much effect contraception actually has (it seems to

be marginal) and how much effect it could have if spacing preferences were realized (which is the

subject of this study). To the extent that family planning programs are focused on rates of population

growth as well as on reproductive health, the answer to this question is an important policy issue.
20

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