Commentary: Did Preston underestimate the effect of economic development on mortality?

Abstract

This raises the question whether Prestons analysis may have underestimated the mortality effects of economic development. I argue that although Prestons article is admirable for utilizing readily available evidence in a new but obvious way to estimate the relative contribution of economic factors to increases in life expectancy during the twentieth century its main conclusion that income has been a trivial factor in recent mortality trends1 is indeed likely to be exaggerated. Helped by Prestons own critical discussion of the findings most epidemiologists will have little difficulty in identifying the main weakness of the analysis. While the article is consistently couched in causal language (e.g. contribution to mortality decline sources of mortality decline influence on mortality decline) it is based on a cross-sectional study design without control for confounding variables. It translates the crude cross-sectional association (between variations in national income and variations in national life expectancy) into a longitudinal inference (about how growth in income leads (or does not lead) to growth in life expectancy). (excerpt)