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

Abstract

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.

Contraceptive use and lengthening birth intervals in rural and urban Eastern Africa

“…We have also shown that long birth intervals are concentrated among, but not limited to, women who report having used a modern method of contraception. Taken together with our findings on the relationship between education and interval lengthening (Towriss and Timaeus 2017), we see that long birth intervals are undoubtedly a feature of the fertility transition in the region. The results of this study suggest that the trends of lengthening would be even more dramatic if access to contraception were improved.…”

“…A number of approaches have been proposed to examine trends in birth intervals that are designed to control for the effects of selectivity and censoring. These include the life-table method (Hobcraft and McDonald 1984;Hobcraft and Rodríguez 1992;Rodriguez and Hobcraft 1980), a paired-cohort truncation approach (Brass and Juárez 1983), and the regression method approach (Moultrie, Sayi, and Timaeus 2012;Towriss and Timaeus 2017). This study adopts the third, regression model approach, since it is more straightforward and flexible than the Brass and Juárez approach and is statistically more powerful than the life-table approach.…”

“…Additionally, all four countries have undertaken four or more DHS and have large urban sample sizes. The analysis of birth intervals using incomplete maternity history data -such as those in the DHS -requires carefully specified techniques because of problems arising from selection bias and the censoring of open-ended intervals (for a full discussion of these issues see Towriss and Timaeus 2017). A number of approaches have been proposed to examine trends in birth intervals that are designed to control for the effects of selectivity and censoring.…”

“…A variable identifying whether a woman had ever been married was included in the model and was interacted with time, in order to allow the effect of a woman having ever been married to vary over time. In order to allow the distribution of interval lengths to change over time, interactions between calendar time and interval duration (measured continuously), interval duration squared, and the log of interval duration were included in the model (Timaeus and Moultrie 2013;Towriss and Timaeus 2017). Finally, to allow for the possibility of changes in parity-specific limitation, parity and calendar time were allowed to interact with each other.…”

Pathways to Low Fertility: 50 Years of Limitation, Curtailment, and Postponement of Childbearing

“…Our work adds to the empirical findings of previous research on this topic in several ways. First, following Towriss and Timaeus (2018), we examine trends in parity progression as well as in the length of birth intervals. Second, unlike Moultrie et al (2012), we look at all the world regions that have been undergoing fertility transition during the last 50 years.…”