The July 2002 article by Daly et al. on optimal indicators of socioeconomic status (SES) for health research is a valuable contribution to the literature on SES and mortality.1 We agree wholeheartedly that it is crucial to measure economic indicators such as income and accumulated wealth to reflect SES adequately in health studies. However, we would like to suggest an important clarification.
The authors acknowledge that associations between SES and health can vary with the social group being examined. In addition, we believe it is important to note that considerable evidence shows that associations between SES and health can also vary with the health indicator being examined.2–8 Thus, SES measures that are optimal for studies of mortality are not necessarily optimal for studies of other indicators of health status, health-related behaviors, or health care use, and optimal SES measures may vary for mortality due to different causes.
Selecting optimal indicators of SES requires considering, in an outcome-specific manner, the likely causal pathways and all potentially relevant socioeconomic factors—such as measures of income, accumulated wealth, power, class, education, and occupation, measured at the individual, household, and community levels and at different times in the life course—on those pathways. If a socioeconomic factor is potentially relevant, its contribution to variation in the outcome should be assessed; if, as often occurs, this is impossible because data on that factor are lacking, the limitation—and how it could affect conclusions—should be acknowledged. Optimal SES indicators cannot be prescribed generically across all health outcomes.
We want to underscore our agreement on the importance of measuring economic indicators in health research, and we do not want this discussion to obscure that crucial issue. However, the reason for including economic indicators is not that every health indicator is invariably associated with them. On a priori grounds—based on ethical concerns about distributive justice and on overwhelming evidence of wealth as a key determinant of health for so many health outcomes in so many settings—it is important to ask the question, How do health and health care vary by wealth? regarding all health and health care indicators. And, as Daly et al. suggest, education and occupation may not adequately reflect income and wealth; this is particularly true among younger or racially/ethnically diverse populations.7
References
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