A Mixture Model for Finite But Unbounded Human Lifetimes

Abstract

Close analysis of an extensive data set combined with independent evidence prompts our proposal to view human lifetimes as individually finite but collectively unbounded. We formulate a model incorporating this idea whose predictions agree very well with the observed data. In the model, human lifetimes are theoretically unbounded, but the probability of an individual living to an extreme age is negligible, so lifetimes are effectively limited. Our model incorporates a mortality hazard rate plateau and a late-life mortality deceleration effect in conjunction with a newly observed advanced age mortality acceleration. This reconciles many previously observed effects. The model is temporally stable: consistent with observation, parameters do not change over time. As an application, assuming no major medical advances, we predict the emergence of many individuals living past 120, but due to accelerating mortality find it unlikely that any will subsequently survive to an age of 125.