Frailty in Transition: Variation and Vulnerability in Aging Populations

Engelman, Michal, Vladimir Canudas-Romo, and Emily M. Agree
Working paper no. 2013-10


This paper asks how the demographic and epidemiologic transitions of the past century and a half have influenced patterns of survival and health in aging populations. We hypothesize that survival improvements at younger ages may yield an older population with a more heterogeneous health profile relative to previous cohorts with higher early-life mortality. To test this hypothesis, we develop a theoretical and statistical rationale for a frailty model designed to examine changes in the composition of successive aging cohorts. The model incorporates a cohort-specific frailty indicator into an equation describing the mortality hazard trajectory across the full lifespan, and its parameters are estimated using life table data for cohorts born 1885-1919. The findings indicate that more recent cohorts are more homogeneous with respect to the timing of mortality than earlier ones—but also less selected, as death culls fewer individuals in early life. We argue that due to ongoing survival improvements, delayed mortality selection has shifted disparities into later life, where they manifest in increasing mortality variability and growing heterogeneity in health.