Trajectories of extreme survival in heterogeneous populations.

In this paper, we analyse the mortality trajectories of French women born between 1820 and 1879. A classic frailty model and a mixture frailty model accounting for individual differences both in the level of mortality and in the rate of aging have been applied. The survival trajectories obtained with these models have been used to estimate the maximum life span. Moreover, a non-parametric approach has been applied to female centenarians born in France between 1870 and 1879 to estimate the extreme age at death. Results confirm that population heterogeneity can be an important factor in the dynamics of mortality at the oldest ages. In particular, the mixture frailty model may fit the data better and estimate the possible maximum life span more accurately. A tendency in favour of an increasing human life span clearly emerges, without however identifying whether a limit in fact exists.