Understanding Population Mortality and Demographic Heterogeneity from a Two-Process Vitality Model

Ting Li, University of Washington
James Anderson, University of Washington

The model established in this work is trying to understand population mortality through two interactive stochastic processes: the intrinsic process defines the survival capacity (vitality) of an organism declines as a Wiener process and hits a zero-boundary where intrinsic death occurs; the extrinsic process assumes extrinsic mortality as the intensity of external challenges exceeding the internal vitality level. With the parameter framework, the model is able to fit mortality data for the entire human life from infants up to 110 years old. With a realistic heterogeneity structure, the model is capable of assessing mortality heterogeneity within a population. And with the construction of two processes, the model can also conduct mortality partition which allows direct analysis of senescence process. Unlike the Strehler and Mildvan (SM) theory, the model can be applied to both period- and cohort-based human mortality data to explore survival patterns without artificial constrains on the parameters.