Future inequalities in life expectancy in England and Wales

Abstract

We noted with interest the much greater increase in life expectancy for men than for women in England and Wales forecast to 2030 by James Bennett and colleagues (July 11, p 163). The expected rate of increase in life expectancy for men not only far exceeds the rate of increase in world-record life expectancy (4 months per year according to Bennett and colleagues vs 3 months per year according to the increase in world-record life expectancy), but also induces a sharp reduction in the life expectancy gap between the sexes towards values that could be considered biologically implausible. Although the authors primarily aim to predict mortality consistently at the subnational level, these sex-specific inconsistencies at the national level reveal substantial shortcomings of their model. The inconsistencies are probably due to the choice of an age–period– cohort model that was fitted to a short reference period, separately for men and women. This complex model was preferred over simpler models because of its smaller error in an out-of-sample forecast in the years 2002–12. In the presence of strong temporal serial correlation, such validation approaches tend to be biased towards the selection of models that are too flexible, potentially resulting in overfitting. Thus, the model is particularly sensitive towards the choice of the reference period, inducing a misleading extrapolation of short-term fluctuations into the future. More coherent and robust forecasts could be generated with a hierarchical model that jointly estimates parameters at different levels of aggregation, such as country, gender, and region, and, if applicable, also accounts for the diff erential eff ect of the smoking epidemic.