Sources of Population Aging in More and Less Developed Countries

We provide the first global assessment of the sources of population aging by tracing its origins to the demographic histories of more and less developed countries. In more developed countries, improvements in survival among successive cohorts have accounted for the large majority of the recent increase in the population's mean age. Improved survivorship and declines in the growth rate of births have made roughly equal contributions to the aging that is occurring in less developed countries. Aging is more rapid in less developed countries because the number of births has declined faster, with China and India making large contributions. Use of the proportion of the population above age 65, 70, or 75 as measures of aging produces results similar to those using the mean age. Mortality decline becomes an even larger contributor to aging using all these measures, and its contribution grows as age advances.