Relation between income inequality and mortality: empirical demonstration

Objective To assess the extent to which observed associations at population level between income inequality and mortality are statistical artefacts. Design Indirect "what if" simulation by using observed risks of mortality a t individual level as a function of income to construct hypothetical state level mortality specific for age and sex as if the statistical artefact arg ument were 100% correct. Setting Data from the 1990 census for the 50 US states plus Washington, DC, were used for population distributions by age, sex, state, and income rang e; data disaggregated by age, sex, and state from the Centers for Disease C ontrol and Prevention were used for mortality; and regressions from the nat ional longitudinal mortality study were used for the individual level relat ion between income and risk of mortality. Results Hypothetical mortality while correlated with inequality (as amplied by the logic of the statistical artefact argument), showed a weaker associ ation with states' levels of income inequality than the observed mortality Conclusions The observed associations in the United States at the state lev el between income inequality and mortality cannot be entirely or substantia lly explained as statistical artefacts of an underlying individual level re lation between income and mortality There remains an important association between income inequality and mortality at state level over and above anyth ing that could be accounted for by any statistical artefact. This result re inforces the need to consider a broad range of factors, including the socia l milieu, as fundamental determinants of health.