Demographic drivers of population ageing

The size and age composition of a population are determined jointly by three demographic processes: fertility, mortality and migration. Fertility levels and trends determine the size of each birth cohort; while mortality levels and trends determine what proportion of those cohorts eventually survive to old age. Age patterns of immigration and emigration also influence the age distribution of the population, although to a lesser extent than fertility and mortality in most countries. This chapter describes the relationships between the three main demographic processes and population ageing, drawing primarily upon United Nations population estimates and projections from World Population Prospects: the 2015 Revision.

Sustainable Development Goals:

Good Health and Well-Being

Reduced Inequalities

Peace, Justice and Strong Institutions