Patterns of Mortality Increase in Late-Middle and Early-Old Age

Ting Li, University of North Carolina at Chapel Hill

Deviations from the Gompertz law of exponential mortality increases in late-middle and early-old age are commonly neglected in overall mortality analyses. In this study, we first examined mortality increase patterns between age 40 to 85 from 16 low-mortality countries, and demonstrated sex differentials in these patterns which also change across period and cohort. These results suggest that the interaction between aging and death is more complicated than the Gompertz law had suggested and also challenge existing biodemographic hypotheses about the origin and mechanisms of sex differences in mortality. We then propose a two-mortality-process model that explains these patterns as the change in the composition of intrinsic and extrinsic death processes with age. We show that the age pattern of overall mortality and the population heterogeneity therein are possibly generated by multiple dynamics specified by the two-process mortality model instead of a uniform process throughout most adult ages.