Income inequality has been shown to be associated with mortality across US states, i.e. more unequal states have higher mortality. Recent survey results have also shown a significant variation on depression prevalence across the US state, and depression has been shown to increase morbidity and mortality.

To measure the effects of income inequality on mortality taking in account depression prevalence.

To test whether the relation between income inequality and mortality found among US states is due to different rates of depression.

Data comes from the US Census Bureau (income inequality) and from the Center for Disease Control (mortality and depression prevalence). Simple and multiple linear regression models were estimated.

Income inequality is positively associated with mortality across US states (p = .039). Depression prevalence was strongly associated with mortality across US states (p < .001). in a multiple regression model including income inequality and depression prevalence, the effect of income inequality is no longer statistically significant (p = .79) while depression prevalence remains significant (p < .001).

Depression prevalence accounts for the inequality effect and is a powerful predictor of mortality variation across US states.