The Threshold between Compression and Expansion of Mortality

Zhen Zhang, Max Planck Institute for Demographic Research

As a result of the steady increments in life expectancy and the relatively slow increase of the maximum lifespan, mortality compression is generally hard to avoid. However, empirical findings are mixed, both for and against compression. In this study we develop a method that allows us to closely investigate the dynamic process of mortality compression. It turns out that there exists a "threshold age", say A*, such that reductions in mortality before it lead to mortality compression, whereas those after age it to mortality expansion. The overall effect of mortality reduction on compression can thus be decomposed into two components, the compression of deaths at younger ages and the expansion of deaths at older ages. Whether the compression of mortality occurs in the whole population depends on which component is greater.