اپیدمیولوژی افتراقی: بهره هوشی، روان رنجوری و بیماری مزمن در 50 ایالت آمریکا

Current research shows that geo-political units (e.g., the 50 U.S. states) vary meaningfully on psychological dimensions like intelligence (IQ) and neuroticism (N). A new scientific discipline has also emerged, differential epidemiology, focused on how psychological variables affect health. We integrate these areas by reporting large correlations between aggregate-level IQ and N (measured for the 50 U.S. states) and state differences in rates of chronic disease (e.g., stroke, heart disease). Controlling for health-related behaviors (e.g., smoking, exercise) reduced but did not eliminate these effects. Strong relationships also existed between IQ, N, disease, and a host of other state-level variables (e.g., income, crime, education). The nexus of inter-correlated state variables could reflect a general fitness factor hypothesized by cognitive epidemiologists, although valid inferences about causality will require more research.

The study of individual differences — differential psychology — has recently expanded to include the study of differences across groups of people categorized by shared geography (e.g., states or nations). Aggregate-level measures now exist for both intelligence (IQ) and the Big Five personality traits ( Lynn and Vanhanen, 2002, McDaniel, 2006 and Rentfrow et al., 2008). These aggregate-level measures seem to consistently predict important geo-political outcomes, as reviewed below. The goal of the present study is to illustrate the unique capacity aggregate-level psychological variables possess in predicting disease rates across populations (here, the 50 U.S. states). These relationships persist even after controlling for state income levels, and for various health-related behaviors (smoking and exercising) that epidemiologists typically study as disease antecedents. Because we consider both dispositional and cognitive traits, we term this area differential epidemiology (as opposed to either dispositional or cognitive epidemiology — for the latter, see, e.g., Deary, 2010). We begin by reviewing the predictive value of both IQ and the personality trait, neuroticism (N), measured for individuals and for geo-political units.