Fig. 1

Model diagrams of three population models of increasing complexity. Three models were compared in the study, of increasing complexity. The simplest model (a) was stratified by age and urban/rural residence and included only fertility and mortality rates and their secular trends, aggregating populations across all educational attainment categories and ignoring migration. The next model (b) included stratification by educational attainment categories (0, 1–5, 6–12, or >12 years of schooling) and secular trends in educational attainment, but ignored migration. The most complex model (c) included migration rates and secular trends in migration rates