Income inequality and health: What does the literature tell us?

This paper reviews the large and growing body of literature on the apparent ly negative effects of income inequality on population health. Various hypo theses are identified and described that explain the empirically observed a ssociation between measures of income inequality and population health. We have concluded that data from aggregate-level studies of the effect of inco me inequality on health, i.e. studies at the population and community (e.g. state) levels, are largely insufficient to discriminate between competing hypotheses. Only individual-level studies have the potential to discriminat e between most of the advanced hypotheses. The relevant individual-level st udies to date, all on U.S, population data, provide strong support for the "absolute-income hypothesis," no support for the "relative-income hypothesi s," and little or no support for the "income-inequality hypothesis." Result s that provide some support for the income-inequality hypothesis suggest th at income inequality at the state level affects mainly the health of the po or. There is only indirect evidence for the "deprivation hypothesis," and n o evidence supports the "relative-position hypothesis." Overall, the absolu te-income hypothesis, although >20 years old, is still the most likely to e xplain the frequently observed strong association between population health and income inequality levels.