Aging and age selectivity: Exploring differences across time and space

Abstract

This paper uses the methodology of the Characteristics Approach to the study of population aging to produce a framework in which population aging is consistently measured from both a cross-sectional and longitudinal perspective. To do this, it introduces the Retrospective Survival Age Threshold (RSAT) to complement the existing Prospective Old-Age Threshold (POAT). The Prospective Old-Age Threshold (POAT) is the forward-looking age at which remaining life expectancy is 15 years. The Retrospective Survival Age Threshold (RSAT) is a backward-looking age reflecting the age by which 79 % of adults (20 + ) have survived. These complementary thresholds, when used together, illuminate variations in trajectories of aging across different mortality regimes. Drawing on national and global data, we show that some countries exhibit parallel movement of POAT and RSAT (implying the expansion of the survival curve), while others display divergent trends linked to shifts in midlife mortality (often implying compression of the survival curve). Our results underscore how combining forward-looking and backward-looking ages can provide richer insights into aging processes than using chronological age alone.