Hidden heterogeneity poses serious challenges to survival analysis because the observed (aggregate) and the unobservable (individual) hazard functions may differ markedly from each other. The recent discovery of the “mortality plateau” has brought new insights and pushed towards the use of the gamma-Gompertz model. However, among the assumptions of this model one, the constancy of the rate of ageing, does not pass empirical tests: the rate of ageing vary (albeit only slightly) by age, gender, birth cohort and country. We propose a new model (EGG) which overcomes this limitation by allowing the rate of ageing to increase gradually with age before converging to a constant value. While preserving all the fine theoretical and empirical properties of its simpler predecessor, the EGG model adapts better to the mortality profile of the cohorts born between 1820 and 1899 in five countries with high-quality data.
Presented in Session 167. Modeling Mortality