The demographic transition in Southern Africa : reviewing the evidence from Botswana and Zimbabwe
Part, but not all, of the observed decline in the number of children ever born reported in the 1984 Contraceptive Prevalence Survey (CPS) and the 1988 Demographic and Health Survey (DHS) in Botswana and Zimbabwe can be attributed to differences in sample composition: Women in the 1988 survey appear to be better educated than women of the same cohort in the 1984 survey. Blanc and Rutstein argue that differences in education levels in the pairs of surveys are not significant. However, weighted Kolmogorov-Smirnov statistics, a comparison of average years of schooling, and the proportions of women who complete primary school or attend secondary school all indicate that the differences are, in fact, significant. This is true in both Botswana and Zimbabwe. Blanc and Rutstein also claim that these differences do not account for any of the observed decline in fertility between the surveys of women age 15 to 49. Their methodology follows cohorts of women rather than age-groups and thus cannot possibly address this issue. Furthermore, to interpret their results, response error and respondent education must be uncorrelated: This is a key assumption that is violated by the data. The authors stand by their conclusions and argue for caution when aggregate statistics from the CPS and the DHS are used to make projections about the course of fertility and population growth in Botswana and Zimbabwe.