Decomposing changes in life expectancy: Compression versus shifting mortality

In most developed countries, mortality reductions in the first half of the 20th century were highly associated with changes in lifespan disparities. To understand the effect of compression and shifting dynamics on mortality changes, the authors quantify the gains in life expectancy due to changes in lifespan variability and changes in the mortality schedule, respectively. They introduce a decomposition method using newly developed parametric expressions of the force of mortality that include the modal age at death as one of their parameters. Their approach allows them to differentiate between the two underlying processes in mortality and their dynamics. An application of their methodology to the mortality of Swedish females shows that, since the mid-1960s, shifts in the mortality schedule were responsible for more than 70% of the increase in life expectancy. The decomposition method allows differentiation between both underlying mortality processes and their respective impact on life expectancy, and also determines when and how one process has replaced the other.