Period Versus Cohort Life Expectancy

Abstract

Mortality can be analyzed according to two main frameworks: the cohort framework, which takes into account mortality risks as they unfold along the actual life cycle of a group of individuals born during the same period of time, and the period framework, which takes into account risks experienced by different cohorts during a single period of time. These frameworks provide two alternative ways for studying life expectancy. Analysis of time trends in life expectancy will differ depending on whether it is calculated by period or cohort. This chapter reviews the extent to which period and cohort life expectancies can be interpreted in terms of underlying health conditions for the corresponding periods and cohorts. While cohort life expectancy is an adequate indicator of a cohort’s underlying health conditions, the connection remains elusive in the case of period life expectancy. Cohort influences and heterogeneity, in particular, appear to generate period life expectancy values that may not entirely reflect period conditions. This chapter also discusses a third and intermediate approach, the cross-sectional cohort approach, which offers some additional insights about the dynamics of mortality.