A Bayesian Model of Later Life Mortality Trends and Implications for Longevity

Abstract

Using a novel, flexible and easily interpretable dynamic Bayesian state space model, we analyze historic and future longevity trends across 18 high income countries over the last one hundred years and 16 large population emerging markets from 1950. Our results show the key driver of global life expectancy is now late-life mortality whose importance is projected to increase further. We find no sign of any impending limit to average life expectancy but project a slowdown in future life expectancy gains despite continuing improvement in later-life mortality. Gains to later-life mortality are increasingly driven by the modal age of death with a slowdown in improvements in the speed of ageing and compressions of mortality. The consequence is a projection increase in the upper bound of age at death and a slowdown in lifespan equality improvements. Whereas the 20th century saw widespread cross-country convergence in longevity indicators the projections are for divergence both within high income countries as well as large population emerging markets. A particular outlier is the United States where our model predicts substantial increases in the modal and upper bound for observed age at death but only small improvements in life expectancy and so an increase in lifespan inequality.

Keywords: Bayesian Methods, Life Expectancy, Lifespan, Lifespan Equality, Longevity, Mortality, State Space Models