Is life expectancy really falling for groups of low socio-economic status? Lagged selection bias and artefactual trends in mortality

Recent public health studies made headlines,1–3 reporting that for some subpopulations in the USA, mortality rates have been higher and life expectancies lower for recent compared with earlier time periods.4–7 These patterns have been described in both popular and academic discourse as a ‘rise’ in mortality or a ‘decline’ in life expectancy. We suggest that it is long past time to admit an alternative—and arguably more plausible—interpretation of these patterns. The fact that a measure was computed at two different time points does not, by itself, make the difference between them a trend. Imagine if researchers measured the average temperature for the whole of the USA a decade ago, and then for only Alaska this year, and found the former number to be lower than the latter. Would it be appropriate to say that average temperatures had ‘declined’ over the decade? We argue that it would not, and that it is likewise not appropriate to be describing many of the observed differences in subgroup life expectancy or mortality as ‘trends’. Nevertheless, scholars and journalists alike have quickly adopted this ‘trend’ conclusion and given short shrift to an alternative interpretation that we find far more plausible. Here, we make the case that this alternative explanation should be the subject of serious empirical investigation and discussion in scholarly and public discourse, rather than getting the treatment it gets now—which is a cursory dismissal relegated to the ‘limitations’ sections of academic papers. We take seriously the reality of health disparities in the USA and the research and policy attention that they demand; understanding and redressing these disparities requires that trends be accurately characterized.