The Deviant Dynamics of Death in Heterogeneous Populations

Abstract

The members of most populationsgradually die off or drop out: people die, machines wear out, residents move out, etc.In many such "aging" populations, some members are more likely to "die" than others.Standard analytical methods largely ignore this heterogeneity; the methods assume that all members of a population cohort at a given age face the same probability of death.This paper presents some mathematical methods for studying how the behavior over time of a heterogeneous cohort deviates from the behavior o f the individuals that make up the cohort.The methods yield some startling results: individuals age faster than cohorts, eliminating a cause of death can decrease life expectancy, a cohort can suffer a higher death rate than another cohort even though its members have lower death rates, and cohort death rates can be increasing even though its members 'death rates are decreasing.