Demographers have studied the determinants and characteristics of these transitions. There are useful robust analyses of the age pattern of fertility, mortality, and migration, as well as their determinants. Analyses of the determinants of demographic change include studies of proximate determinants, as well as broader explanations in terms of social, economic and cultural processes. The age structure of population is known to be an outcome and a summary index of its history of fertility, mortality and migration. The concept of population momentum captures the essential inertia of age-structural changes .
Public policy is concerned with a spectrum of decision-making.
The linkages between population age structure and public policy may be illustrated by taking education as an example. It is well documented that education is a powerful determinant of fertility, mortality and migration. Also, largely as a consequence of policy concerning human capital and economic development, most countries today evidence increases over time in school enrolment, and in educational attainment of those who enroll, resulting in upward trends in the educational attainment of populations. The most elementary relationship between age structure and policy is that demand for education services will be high when the age structure of the population is young, with obvious corollaries regarding populations in transitions. Gender gaps have implications for gender differences in political and economic power, control over reproductive rights, economic well-being, and so on, and bear on policy in several areas.