Analysis of oldest-old mortality:: Lifetables revisited

This paper provides a data analysis and some methodological advances which contribute to an ongoing scientific debate about the patterns of aging. One of the problems we address is how to estimate a hazard function when only aggregated information on the lifetimes in the form of a lifetable is available. This problem affects the estimation of oldest-old mortality which in turn plays an important role in the quantification of biological lifespan and longevity. We illustrate these issues with an analysis of mortality data obtained from cohorts of nematodes. The methods involve data transformation with the aim of bias reduction when estimating the hazard function. We provide rigorous asymptotic results for the smoothing of lifetables and show that the transformation approach is supported by both asymptotic and simulation results. We also demonstrate how the information contained in many samples of lifetables, as typically obtained in aging experiments, can be summarized in a two-dimensional hazard surface.