We appreciate Dowd and Hamoudi’s comments regarding our editorial. Their commentary reflects the critical thinking and productive dialogue that we had hoped to generate.
Dowd and Hamoudi express concern that we have “forced the inquiry into a dichotomy of ‘composition versus causation.’” However, we do not consider these explanations to be dichotomous as they are neither mutually exclusive nor contradictory. Rather, we stated that these explanations can be intertwined and jointly contribute to recent trends.1 The causation–composition framework we proposed is akin to the social causation–selection framework widely used since the 1970s.2,3 Understanding whether socioeconomic disparities in health are attributable more to causation or selection has been called “the classical epidemiological issue.”2(p946) As our collective understanding of the mortality trends matures, a more nuanced set of explanations may emerge, but for now we believe the causation–composition framework is appropriate.
Citing two analyses that used an alternative method for examining mortality trends by education level,4,5 Dowd and Hamoudi claim that no education group has experienced absolute declines in life expectancy. The cited commentary4 and conference proceeding5 examined equivalent percentiles of education groups over time. To create an equivalent group of low-educated adults in two time periods, this method adds some high school graduates to the group of nongraduates in the latter period so that the combined group is proportionally equal in size to nongraduates in the earlier period. However, a broader look at peer-reviewed studies using this method reveals inconclusive evidence; a number still find the mortality trends we describe among low-educated women.6,7 We also note a potentially problematic assumption at the core of this method. By combining graduates with nongraduates, the implicit assumption is that graduating high school has no effect on mortality. In essence, the method replaces one potential source of heterogeneity (compositional changes among nongraduates over time) with another (different educational experiences among the combined group).
We agree with Dowd and Hamoudi that it is time to move beyond current approaches to better understand the mortality trends. Scholars are increasingly using new and more sophisticated approaches, such as age-period-cohort analyses,8 propensity scores,6 and, as in Dowd and Hamoudi’s analysis, simulations.9 Studies should also aim to explain why the unfavorable mortality trends among low-educated adults are, by in large, not occurring among men.
We look forward to further discussions and collaborations to explain the perplexing trends in mortality, and value Dowd and Hamoudi’s contribution to the conversation.
References
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