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.     

Findings and implications of a correlation analysis of the closed and the open birth intervals

A correlation analysis of data on four fertility variables viz. closed birth interval, open birth interval, age and parity, collected in a survey of about 2,000 married women in the reproductive ages in rural India, is carried out in order to study the interrelationships among these variables. Two hypotheses are formulated governing the relationship of the closed and open birth intervals with the fecundability distribution of fertile women, and Parity Progression Ratios which are largely influenced by the proportion of women becoming sterile after each parity. The data lend support to the hypothesis that while the closed intervals are influenced mainly by the distribution of fecundability of women of non-zero fecundability, the open birth intervals are influenced mainly by Parity Progression Ratios or the proportion of women becoming secondarily sterile after each parity. The analysis suggests that we can use the mean open intervals of women classified by parity as indices of fertility, and such an index is comparable to the index of average age of women of given parity. In areas where it is difficult to ascertain the correct age of women this might be of practical value.     

Fertility change in five Latin American countries: A covariance analysis of birth intervals

This paper analyzes patterns of childbearing throughout the reproductive career of Latin American women, using a hazards model of birth interval life tables. Data come from five fertility surveys of the World Fertility Survey Programme. The analysis, within each country and across time, assesses how demographic factors of reproduction influence the fertility history of women throughout their reproductive lives.     

Some problems observed in the 1 percent sample survey of fertility in Shanghai]

From July to December of 1982, a sample survey of fertility was conducted of childbearing females between the ages of 15 and 49 in Shanghai. The results of this survey can be summarized by the following points: (1) The percentage of females of childbearing age is very high, and the situation in the suburbs is even more serious than that inside the city. This is the major reason for a large scale population increase in Shanghi. (2) The marriage rate is high, the divorce rate is low, and the people who remain single in their lifetime are few. This stable family and marriage situation provides a favorable condition for population growth. (3) The average marrying age for childbearing females has gradually risen in recent years, but this trend is now reversed. More and more people are getting married when they are young. (4) Fertility for childbearing aged females decreases according to the increase in their age. In the last two years, however, this downward trend has been reversed, and fertility is gradually increasing again. The above points show that family planning and birth control have entered the most crucial period in Shanghai. Efforts and enforcement should be strengthened in the area of family planning, and no relaxation should be allowed so that the goal of controlling rapid population growth may be achieved.     

Land use as a mediating factor of fertility in the Amazon

Despite implications for both humans and the environment, a scant body of research examines fertility in forest frontiers. This study examines the fertility–environment association using empirical data from Ecuadorian Amazon between 1980 and 1999. Fertility dramatically declined during this period, and our empirical models suggest that households’ relationship to land partially explains this decline. Controlling for known fertility determinants such as age and education, women in households lacking land titles experienced a 27 % higher birth rate than did women in households with land titles. This suggests insecure land tenure was associated with higher fertility. Furthermore, each additional hectare of new pasture was associated with a 16 % higher birth rate, suggesting the potential role of a more stable and lucrative income source in supporting additional births. Findings from this research can help inform strategic policies to address sustainable development in frontier environments.     

Note on the use of statistics of total fertility to provide estimates of crude birth rates

It is shown that estimates of the total fertility by age of mother can be used to give good rough approximations to birth rates in under-developed countries and that this method is likely to be more accurate than the collection of historical data relating to particular calendar periods.     

Nuptiality and fertility of birth cohorts

The impact of changes in age patterns of nuptiality on the net reproduction rate is examined using life table techniques and assuming that age-specific fertility within marriage and fertility outside of marriage are fixed. In the second section, a standardization technique is used to investigate the impact of changes in nuptiality on age-cumulative measures of marital fertility. Examples using data for selected generations of Australian women demonstrate the extent to which recent changes in average completed family size in Australia were affected by changing nuptiality patterns.     

Determinants of birth intervals and their means

Abstract 1. The duration of post-partum infecundity; 2. Fecundability; 3. Duration of pregnancy.     

Some problems found in a retrospective survey of fertility in Haidian district, Beijing]

The results of a fertility survey undertaken in the Haidian district of Beijing, China, in 1981 are presented. The data are from a random sample of 6.3 percent of the population at selected ages. The results show an increase in age at marriage, a decrease in the interval between marriage and first birth, and a decrease in the number of pregnancies associated with the family planning program.     

Values and fertility change in Japan

This paper analyses how value change and economic and social change have jointly affected fertility in Japan since 1950, and especially since 1973 when fertility resumed declining after some 15 years at near-replacement level. The resumption of fertility decline since 1973 has been driven primarily by underlying economic and social changes. Value change has tended to lag behind fertility change, and this lag has tended to be larger in Japan than in other advanced nations, primarily because underlying economic and social conditions have evolved more rapidly in Japan, and because it takes time for values to adjust to changes in underlying conditions. Because of Japan's high degree of cultural homogeneity, values tend to be widely and quickly shared, so that under certain conditions value change tends to occur in spurts. In Japan, many of the more important value changes affecting fertility in recent decades are bound up with major educational and job gains by women, which have led to greater economic independence and more emphasis on values of individualism and equality between the sexes.     

Interpreting demographic effects in duration analyses of first birth intervals

Estimated demographic effects in proportional hazard models of first birth intervals could reflect time-invariant differences in the risk of a birth, or differences in the timing of a shift in the risk, or both. This paper attempts to distinguish between these possibilities. The procedure is to estimate a more general model than the proportional hazard specification, in which the evolution of the risk of a birth can differ with demographic characteristics. The proportional hazard specification is nested within this more general model. Consequently, the consistency of the data with the risk or the timing interpretation of demographic effects can be tested. The data studied do not lead to a rejection of the proportional hazard specification.Department of Economics, University of Pennsylvania. The initial stage of this research was supported by a National Science Foundation Graduate Fellowship. I have benefited from insightful comments from David Bloom, Andrew Foster, Zvi Griliches, V. Joseph Hotz, Duncan Thomas, anonymous referees, and participants in seminars at Harvard University and the University of Pennsylvania, and in the Economic Demography sessions of the 1988 Population Association of America annual meetings. Any remaining errors are my own.     

Some aspects of the use of birth expectations data from sample surveys for population projections

The value of national sample survey data relating to birth expectations for projecting births is reassessed in the light of data limitations pointed out by Ryder and Westoff among others and of the methods of projection used by the United States Bureau of the Census. The annual level of fertility under the cohort-fertility projection method depends on the assumptions regarding completed fertility, about which the available survey data are fairly informative, and on the assumptions regarding the timing of births, about which the survey data tell us very little. Test calculations suggest that Ryder and Westoff have overstated the significance of timing relative to completed family size for the level of future births. We believe that the fall in the annual total fertility rate in the first half of the sixties is to be explained only in part by a general delay in childbearing; a moderate to substantial decrease in completed family size has also occurred. Analysis of the latest set of fertility projections of the Census Bureau also suggests that the assumptions about completed fertility are a much more important determinant of the level of future births than timing, both in the short and long term. Although the available expectations data cannot help in predicting short-term annual changes in fertility, they appear useful for making long-term projections of annual fertility. Expansion of the size, frequency, and content of the sample surveys and incorporation of parity and birth interval into the projection method may improve projections.     

Seasonal migration and seasonal variation in fecundabillty: Effects on birth rates and birth intervals

Seasonal patterns in conception rates have been documented in several recent studies. In this paper, a mathematical model of the reproductive process is developed through which the impact of such variation in conception rates is assessed. It is found that the effect on fertility can be quite substantial, but that the birth rate when seasonal variation is occurring is approximated well by the birth rate calculated when conception rates are constant at their mean. These results indicate that further documentation of seasonality in conception rates and exploration of the causes of these patterns and their change is an important area for demographic research.     

Family planning achievements as suggested by changes of total fertility and party birth rate]

The dynamic characteristics of China's 5 distinct stages of population development since the People's Republic of China was established in 1949, namely, 1950-1958, 1959-1963, 1964-1970, 1971-1981, and 1982-present, are outlined and discussed. By tracing both the overall rate of population growth and age-specific fertility rates for women aged 15-45 (5-year groups), a clear pattern emerges which indicates that the rates of early and late fertility (ages groups 15-19 and 30-45) are significantly declining. This is interpreted as a key factor in the overall decline in fertility rate. Annual statistics showing the number of children per woman of childbearing age and interval between 1st marriage and 1st birth are compared and discussed. It is concluded that the overall decline in birth rate and fertility rate since the 1970's is attributable to China's successful family planning campaign.     

Some aspects of mating and fertility in the West Indies

This paper deals with certain problems in fertility analysis in the West Indies that have their origin in two characteristics of the populations involved: the diversity of family forms and the imbalance between the sexes. Considerations of the main features of these family types, in terms of a fourfold classification as well as in terms of the threefold classification adopted at recent censuses (single, common law and married), show that many techniques relied on in the study of fertility among European populations are inapplicable to West Indian populations.

The limited data available permit only rough estimates of the rates of formation of different types of unions: but these emphasise that formal marriage usually takes place late in the childbearing period, generally after the couple has had one-or more children, that the formation of keeper unions begins considerably earlier and that the common law type is a transitional state between the looser keeper union and the state of formal marriage.

There seems to be no chance of studying fertility differentials among the several family types in terms of reproduction rates. Census data however provide three measures for this purpose, all of which show that fertility is highest for the married type and lowest for the single or keeper union. These differentials seem to run counter to the more usual pattern of fertility differentials which show fertility lowest among groups of high socio-economic standing.

Imbalance between the sexes is of importance primarily in the problem of arriving at satisfactory indices of fertility, though it may also have contributed somewhat to the establishment of the pattern of low marriage rates. Wide discrepancies between rates based on males and rates based on females appear, both in respect of fertility levels at given points of time and in respect of fertility trends. These discrepancies seem closely related to the imbalance between the sexes in. the reproductive age span. Under these conditions the use of joint G.R.B's clearly offers a more realistic measure of fertility than rates based on either sex.     

A cohort analysis of the timing of first birth and fertility in Ghana

This paper examines the nature of the inverse association between age at first birth and fertility across successive generations of Ghanaian women. Within the context of enhanced non-marital opportunities for contemporary women and declining fertility, we develop a rationale for and test the hypothesis that in a medium fertility environment as currently found in Ghana, the effect of age at first birth on fertility becomes more important than ever before. Five birth cohorts were identified (1938–1944; 1945–1949;1950–1954; 1955–1959; 1960–1964)from a merged file of the 1988, 1993 and 1998 Ghana Demographic and Health Surveys. The analyses were restricted to women over 35 years old at the time of the surveys, which allowed us to use current parity as a reasonable proxy for completed fertility. Preliminary results suggest that women who had first births early tend to have a higher number of births than those whose first births occur late, regardless of birth cohort. In multivariate analyses, the effect of age at first birth as a determinant of fertility was found to be more substantial among later cohorts. The implications of the findings are discussed.     

Changes in the use of birth control methods

Abstract Information on changes in the methods of contraception used was collected from women in a KAP Survey of Trinidad and Tobago in 1970-71. Using methods analagous to those used in the study of internal migration, it is found that 54% of contraceptors were still using the method they first used, and 46% had changed. In general, the net changes tended to be from less to more efficient methods. This is demonstrated with data showing: 1. the number of changes from one method to another; 2. the number of changes these women have made, considering the first and last methods only; and 3. the number of changes, including intermediate changes. Nevertheless, there is also an appreciable movement away from the more effective methods either to other methods, or out of contraceptive practice entirely. The rate of dropout from contraception has been increasing in recent years for all methods, and, apparently, for all ages of women. The principal reasons given for stopping the use of the various methods were: 1. pregnancy; 2. that the method was uncomfortable or too much trouble; 3. that the method made the user ill (in the case of the pill and the IUD); and 4. that the partner disliked the method (in the case of the condom and withdrawal). More positive reasons include: 1. that the woman wanted more children; and 2. that she no longer had a partner.     

Effect on unwanted fertility of extending physician-administered birth control in the United States

A goal of publicly subsidized family planning programs in the United States is to prevent unwanted births, and the primary means being used to achieve this goal is to increase coverage with physician-administered contraception, with priority being given to persons from low-income families. We analyzed data from families living in low-income neighborhoods to determine whether that means would contribute to that goal, and if so, how much unwanted fertility might be decreased through increased coverage with physician-administered methods.The results indicate that increased coverage with those methods would decrease unwanted fertility by 80 percent (79 percent among blacks, 83 percent among whites). Increasing the ratio of sterilization to pill and IUD makes the effect of the increased coverage even more dramatic.