What’s happening to the age at first birth in the United States? A study of recent cohorts

This paper analyzes cross-cohort trends in the age pattern of women at first birth in the United States. The analysis involves fitting the Coale-McNeil marriage model to the age distribution of first birth frequencies for a number of recent white and nonwhite cohorts. Methodologically, the results (a) provide support for the application of the Coale-McNeil marriage model to first birth data, and (b) demonstrate the ability of the model to accurately project first birth fertility for cohorts which have yet to complete their childbearing years. Substantively the results indicate (a) that the proportion of women who will never have a first birth is increasing across cohorts and can be expected to be as high as .25 and .20 for recent white and nonwhite cohorts respectively; (b) that recent nonwhite cohorts have an appreciable number of first births at earlier ages than their white counterparts, as well as a lower mean age at first birth and increasingly less dispersion (across cohorts) in their age at first birth; and (c) that the mean age at first birth and the proportion of first births occurring between ages 25 and 34 is increasing across cohorts of white women but is stable across cohorts of nonwhite women.     

Modelling period fertility: Schooling and intervals following a birth in Eastern Africa

We describe a regression-based approach to the modelling of age-, order-, and duration-specific period fertility, using retrospective survey data. The approach produces results that are free of selection biases and can be used to study differential fertility. It is applied to Demographic and Health Survey data for Ethiopia, Kenya, Tanzania, and Zimbabwe to investigate differential trends in fertility by education. Parity progression fell and the intervals following each birth lengthened between the 1970s and 2000s in all four countries. Fertility fell most among women with secondary education. In contrast to other world regions, postponement of successive births for extended periods accounted for much of the initial drop in fertility in these African countries. However, family size limitation by women with secondary education in Ethiopia and Kenya and longer birth spacing in Zimbabwe also played significant roles. Thus, birth control is being adopted in Eastern Africa in response to diverse changes in fertility preferences.     

Measuring marital fertility control with CPA

Cohort Parity Analysis (CPA) is an indirect method for measuring the extent and timing of the adoption of fertility control within marriage. Cohort Parity Analysis uses 2 sets of parity distributions, 1 from the population under study (the "target" population) and 1 from a similar population in which fertility control is absent (the "model" population). Fertility control is defined as any set of behaviors in the target population that cause its parity progression rates to differ from those of a similar but noncontrolling population. The target population contains an unidentified mixture of controlling and noncontrolling couples for a given age range and marriage duration. The model population is similar in all respects except that it contains no controllers. Examples are taken from urban and rural Irish populations in the 1911 census data. Cohort parity analysis rests on 2 basic assumptions: 1) For every specified marriage duration and marriage age, there exists some parity above which controllers are never found; and 2) Parity progression rates of those in the mixed population who have never initiated fertility control are identical to those in the model population. Further, one must identify a cutoff parity beyond which controllers are presumed not to be found. In these urban Irish examples cutoff parity for each marriage age and duration is set at 20% of that of the noncontrolling rural Irish population. The upper and lower bounds on the percentage of controllers are derived by obtaining the lower and upper bounds on the size of the group at that parity who never controlled and subtracting these estimates from the observed percentage of the target population observed at that parity. Flow charts are used to present the methodology of cohort parity analysis in a simple format. the method is illustrated in the case of Ireland in 1911. Aggregate parity distributions for the county boroughs of Dublin, Belfast, Cork, LOndonderry, Limerick, and Waterford are taken as the target distribution; and parity distributions for those living outside the county boroughs are taken as the model distributions. The analysis shows that 28% of urban-dwelling Irish women who married before age 30 and were married between 4 and 29 years in 1911 used some effective means of fertility control. The parity distributions also show that women who married later controlled their fertility to a greater extent and that between 20.9 and 25.5% of women married 4 years in 1911 had already practiced fertility control by 1911, but only 15.5% of those married 15-19 years had used fertility control by 1911. Cohort Parity Analysis is thus a useful method of examining historical populations in the process of fertility transition.     

Proximate determinants of Philippine fertility: 1983 levels and patterns

Data from the 1983 National Demographic Survey are used to analyze the proximate determinants of Philippine fertility in each of the 3 stages of family formation and to identify all of the direct and indirect factors affecting fertility levels and trends. 10,843 ever-married women and 12,771 children were included. The analysis pertains first to the starting patterns of family formation, the age at first birth, and the proximate determinants (age at menarche, age at first marriage/union, conception before first birth, fetal wastage first birth, interval between first marriage and first birth). Further analysis examines birth spacing patterns including the postpartum nonsusceptible period, the exposure interval and stopping patterns. Almost all births occur within marriage, and childbearing begins late at 22.5 years. However, 15.4% of first births are conceived premaritally. The mean age at first birth increases from younger to older cohorts. Urban women were slightly older (23.0 years) at the birth of their first child. Those with education below the 4th grade had first births 3.5 years earlier. Contraceptive use was low at 1.8% before first birth. Younger cohorts were more likely to use birth control and urban wives were more likely to use it than rural wives. 6.4% reported a first pregnancy ending in nonlive births, which were primarily spontaneous abortions (5.2%), stillbirths (1.0%), and induced abortions (.2%). 5.8% report never having been pregnant and 1.1% never having given birth to a live-born child. 20.4% were childless between the ages of 15-24 years, and 4.6% between 25-34 years. Childlessness was slightly higher among urban women (7.1%) than rural women (6.7%). A decreasing age at menarche has appeared; i.e., 13.6 years for the cohort 15-24 years, and 14.0 for the oldest cohort. By age 15, 82.9% had begun menstruating. The mean age at marriage is early at 20.7 years, and older cohorts tended to marry later at 21.4 years. Urban women marry a year later (21.4 years) than rural women. Lower educated women marry 4 years earlier. The mean length between first marriage and first birth was 18.4 months. In the younger cohorts, spacing patterns are shorter. Postpartum susceptibility is short. Return to sexual relations after a birth occurred at 2.8 months. The exposure time required to conceive is fairly long at 16.6 months and is attributed to contraceptive use, since coital frequency is high and temporary separation is infrequent. The average age at last birth is late at 37.6 years.     

Diverging fertility among U.S. women who delay childbearing past age 30

In this paper I examine the evolving association between educational attainment and the timing of births. In the late 1970s, women with four-year college degrees had lower first birth rates before age 30 than women with less education, but rates of first births were similar for the two groups after age 30. From the 1970s to the 1990s, first birth rates decreased before age 30 for all women, but increased after age 30 only for women with four-year college degrees. Parity 2 birth rates also increased for college graduates with a first birth after age 30. These results document widening educational differences in fertility timing between 1975 and 1995, which may reflect period changes at later ages in women's work and family lives.     

Fertility in Larsmo: The Effect of Laestadianism

Larsmo is a small municipality on the West coast of Finland with an exceptional fertility development due to the presence of a revivalist movement, Laestadianism, which is opposed to contraception. About 40 per cent of the population are Laestadians. Laestadians do not cohabit outside formal marriage, and the rule of pre-marital sexual abstinence seems to be observed. Within marriage, fertility seems to be unrestricted with respect to the first child, but an increasing proportion of Laestadians have begun to practise family planning, lengthen birth intervals, and restrict their families to three or four children. There remains, however, an inner group which appears to procreate without restriction. Since mortality is very low, a total fertility of six births per woman corresponds to a net reproduction of about 2.9, which is among the highest documented after 1970.Fertility in Larsmo has traditionally been high, and we expected that the presence of pro-natalist Laestadians would tend to increase the fertility of non-Laestadians as well. However, the demographic behaviour of non-Laestadians in most respects resembles that of the Finnish population as a whole, although extra-marital cohabitation seems to be rarer, since almost all the children born are legitimate.     

A model of the age patterns of births by parity in natural fertility populations

This research develops a convolution model to express the age patterns of fertility at each birth order in natural fertility populations in terms of six parameters, directly representing the proximate determinants of fertility, and a series of parity level indicators. The parity level indicators at each birth order are simply the proportions of women in a cohort who will eventually have births at each birth order it the age‐related fecundity decline is controlled. The Coale‐McNeil nuptiality model is adopted to represent the age pattern of first marriage rates and the natural fertility schedule employed in the Coale‐Trussell fertility model is incorporated to adjust age effects. The fast Fourier transform is used in solving the model numerically. It proves that the model is able to provide excellent fits to fertility for rural Chinese women in the 1950s.     

Models of contemporary Dutch family building

Summary Recent data suggest that the level of use of oral contraceptives in the Netherlands is perhaps the highest in the world. Moreover, the greatest recent change in family building patterns is the tendency of newly weds to postpone their first birth. A micro-simulation model was developed to test the effect on fertility of such a change. An attempt was made to employ input data compatible with conditions obtaining in the Netherlands, and the distributions of family building patterns were based on recent survey evidence. The aim was not to duplicate Dutch fertility, but rather to estimate the range over which marital duration-specific fertility can be expected to vary with an increase in the proportion of couples who space their first birth. Such an increase was found to lower fertility dramatically after five years of marriage, although completed fertility was seen to vary very little. This result indicates the care that must be taken in ascribing a decline in the fertility of the early years of marriage to an overall fertility decline.     

The negligible influence of premarital cohabitation on marital fertility in current danish cohorts, 1975

This paper studies the influence of premarital cohabitation on marital fertility by applying life table methods to data for cohorts of Danish women born in 1926–1955, collected in retrospective interviews made in 1975. For each five-year cohort, the data have been analyzed by duration of marriage or by duration since previous birth, for women who had no reported births before marriage. Our main empirical results are: (a) that women who married at age 15–19 had higher rates of marital first and second births than those married at ages 20–24, and (b) that premarital cohabitation had very little influence on births of these two first orders in our data.     

Convergence on the two-child family norm in Australia

This paper examines childbearing patterns of ever-married women in Australia and establishes that during the process of fertility transition from high to low levels which largely began after 1971, significant changes occurred in the timing of the first birth after marriage, the length of the first and inter-birth intervals and the proportion of women progressing to have a first birth or births beyond the second. The analysis also confirms the predominance of the twochild family norm and shows the emergence of a converging trend on that family norm. The study applies the life tables technique to the marriage and birth history data collected in the Family Formation Survey conducted by the ABS in September 1986.     

The TFR and birth control]

Total fertility rate if (TFR) is a simple an straight forward measure of women's fertility. However, it is difficult to use the TFR as a target measure in FP programs. If TFR level is set as a target for a particular year, how can women's fertility be regulated to achieve this target? The following analysis suggests a simple model to control the proportion of birth parity. First, the TFR is decomposed into a parity- specific TFR. The parity-specific TFR can be worked out using coefficients of the regression models calculated from data of previous fertility surveys. Once the TFR is given, the parity-specific total fertility can be calculated using a model with coefficients from empirical data. Then the number of births of each parity may be calculated from the parity-specific TFR using the female age structure in a particular year, the survival probability, and the standard fertility model for each parity. When the number of surviving children of each women at child-bearing age is known, the desired proportion of births of each parity can be calculated using the standard birth probability during a years. From these models, it would be possible to calculate how many women can have their first child/year, and how many can have the second. Thus, family planning organizations would be in a position to formulate a birth quota on the basis of the above information.     

A fertility survey in the Maltese Islands

In order to determine whether fertility is declining in Malta, a sample was taken by the Maltese Central Statistical Office in mid-1955, along the line of the Family Census of 1946 in Great Britain. The size of the sample was 10,000, and the response very good. The sample shows no noticeable decline in fertility since the marriage cohorts of the beginning of the century. Some decline is noticeable int he fertility of the later durations of marriage, but completed family size remained more than 6 for the cohorts of the 1920's. This contrasts with the declining fertility shown by the enquiry in Great Britain, and the figure of 6 is in fact much greater than the completed families born to cohorts in Great Britain at the end of Queen Victoria's reign. Fertility seems in fact to be still rising in Malta for the first 18 months of marriage; and the first decade of marriage continues to show an average of 4 births. It seems therefore that the recent decline in the birth rate is to be attributed to changes in the populatino structure rather than in marital fertility. The continued high fertility implies a very rapid rise in population in the absence of emigration.     

Statistical modeling of selected aspects of the childbearing process with application to World Fertility Survey countries

"A mathematical model for estimation of certain aspects of the childbearing process, which requires only data on age-specific fertility rates, is developed. Synthetic maternal childbearing indices, namely, mean ages at first and last birth, length of reproductive life span, inter-birth spacing, and proportion of childless women, in addition to the well-known mean age at childbearing, for the WFS [World Fertility Surveys conducted in developing] countries are obtained using the proposed model. The indices are free from age truncation effects, and, under certain assumptions, provide information about a cohort's completed fertility before the women stop reproducing. The effects of women's residence and education on fertility are also examined." (SUMMARY IN FRE)     

生育水平、性别偏好和出生性别比——兼论出生性别比的监测方法

本研究以马-冯-陈模型为定性基础,认为一定人口的出生性别比并非固定不变,而是受到生育水平的影响。当无性别偏好时,生育水平主要通过改变不同孩次占出生人口比例的方式影响出生性别比;当有性别偏好时,生育水平既影响不同孩次占总出生人口的比例,又影响不同孩次的出生性别比,从而对总出生性别比产生影响。对于没有性别偏好和性别选择行为的人口,生育水平变化是引起出生性别比波动的主要原因。有性别选择行为时,生育水平变化对出生性别比的影响较小,性别选择行为是出生性别比异常的主要原因。监测以"曾生子女孩次和性别次序"为条件划分的人群,可以有效而便捷地判断出生性别比变化趋势。     

The prediction of completed fertility

There has been considerable interest in the relation between familysize desires and completed fertility. Longitudinal data from the Princeton Fertility Study provide a unique opportunity to compare the number of children desired after the birth of a second child to the size of completed families. The average number of children desired by women after the birth of their second child predicts very well the average size of their completed families. The average family size desired at the first interview and average estimated completed family size some eight years later are identical for the total sample, and vary hardly at all within religious or education subgroups. One-third of the variance in the completed fertility of couples is "explained" by wife's family-size desires and the proportion of explained variance increases to two-fifths when we include the husband's first interview desires and the interval between marriage and second birth. Yet in spite of the relatively high correlation between desires and achievement, only 41 percent of these women achieved exactly the number of children they desired at the first interview, while 14 percent had two children more or fewer than originally desired. Nevertheless, data on contraceptive efficiency indicate that desires after the birth of the second child constitute meaningful goals in terms of which the respondents regulate their subsequent behavior-efficacy of contraceptive practice shows substantial improvement after the desired number has been achieved.     

Interrelationships between fertility and marital dissolution: Results of a simultaneous logit model

Previous studies have failed to examine (a) the simultaneity of decisions to bear children and to dissolve a marriage and (b) the effects of the childbearing in the period just before dissolution on the likelihood of disruption. We attempted to resolve both problems by developing a simultaneous logit model of the interrelationship between the probability of separation and of having a birth during this period (when dissolution presumably is being considered). The model was estimated at successive durations of first marriage, using data for white women in the 1970 National Fertility Survey. The results indicate that childbearing patterns— number of children and age of youngest child at the beginning of the marital interval being studied and fertility during the interval—did not influence the likelihood of separation in simple or consistent ways over the marital life course, nor did marital strife (as indicated by separation) seem to affect childbearing throughout marriage.     

Cohort Trends in Premarital First Births: What Role for the Retreat From Marriage?

We examine cohort trends in premarital first births for U.S. women born between 1920 and 1964. The rise in premarital first births is often argued to be a consequence of the retreat from marriage, with later ages at first marriage resulting in more years of exposure to the risk of a premarital first birth. However, cohort trends in premarital first births may also reflect trends in premarital sexual activity, premarital conceptions, and how premarital conceptions are resolved. We decompose observed cohort trends in premarital first births into components reflecting cohort trends in (1) the age-specific risk of a premarital conception taken to term; (2) the age-specific risk of first marriages not preceded by such a conception, which will influence women’s years of exposure to the risk of a premarital conception; and (3) whether a premarital conception is resolved by entering a first marriage before the resulting first birth (a “shotgun marriage”). For women born between 1920–1924 and 1945–1949, increases in premarital first births were primarily attributable to increases in premarital conceptions. For women born between 1945–1949 and 1960–1964, increases in premarital first births were primarily attributable to declines in responding to premarital conceptions by marrying before the birth. Trends in premarital first births were affected only modestly by the retreat from marriages not preceded by conceptions—a finding that holds for both whites and blacks. These results cast doubt on hypotheses concerning “marriageable” men and instead suggest that increases in premarital first births resulted initially from increases in premarital sex and then later from decreases in responding to a conception by marrying before a first birth.     

Cohort estimates of nonmarital fertility for U.S. Women

Historical trends in U.S. nonmarital fertility have been compiled almost exclusively from vital statistics on births. This paper complements this historical record by providing cohort estimates of nonmarital fertility for cohorts of U.S. women spanning approximately 50 years of cohort experience. Life table estimates using retrospective marital and fertility histories in the June 1980, 1985, 1990, and 1995 Current Population Surveys reveal nonnegligible levels of nonmarital fertility historically. For women born between 1925 and 1929, nearly 1 in 10 had at least one nonmarital birth by age 30. For women born between 1965 and 1969, more than 1 of 4 had one or more nonmarital births by age 30, with roughly 1 of5 white, 3 of 5 black, and 1 in 3 Hispanic women having at least one nonmarital birth by age 30. Life table estimates reveal a twofold increase between ages 20 and 30 in the percentage of women with at least one child outside of formal marriage for all cohorts of white and Hispanic women, and an increase of roughly two-thirds for all cohorts of black women. I also document qualitative differences in nonmarital fertility by race/ethnicity, with the percentage of nonmarital births following a divorce or marital separation for white women approximately twice that for black or Hispanic women. Finally, I introduce a new measure, the cohort nonmarital fertility ratio (CNMFR), which provides a cohort complement to the standard period nonmarital fertility ratio. Conservative estimates reveal a roughly threefold increase in the CNMFR for women born from 1925-1929 to 1950-1954 for both whites and blacks, despite substantially higher levels of nonmarital fertility among black women. Overall, these findings reveal surprisingly high levels of nonmarital fertility for women born since the 1920s and confirm that nonmarital fertility has become an increasingly substantial component of overall U.S. fertility.     

Parity patterns of birth interval distribution

A simplified model is presented for the measurement of inter-live birth interval distributions. Comparative analyses of "effective fecundability," the mean length and variation of postpartum infecundity, and the parity progression ratio based on this measurement model are presented using data from U.S. marriage cohorts and from an Indian sample. Parity differentials in these reproduction parameters are investigated, and the ramifications for fertility estimate and projection discussed.