County-level political group density, partisan polarization, and individual-level mortality among adults in the United States: A lagged multilevel study

Objective To investigate the associations between county-level political group density, partisan polarization, and individual-level mortality from all causes and from coronary heart disease (CHD) in the United States. Methods Using data from five survey waves (1998–2006) of the General Social Survey-National Death Index dataset and the County Presidential Election return 2000 dataset, we fit weighted Cox proportional hazard models to estimate the associations between (1) political group density and (2) partisan polarization measured at the county level in 2000 (n = 313 counties) categorized into quartiles and individual-level mortality (n = 14,983 participants) from all causes and CHD with follow-up from one year after survey up until 2014, controlling for individual- and county-level factors. We conducted these analyses using two separate measures based on county-level vote share differences and party affiliation ideological extremes. Results In the overall sample, we found no evidence of associations between county-level political group density and individual-level mortality from all causes. There was evidence of a 13% higher risk of dying from heart disease in the highest quartile of county-level polarization (hazards ratio, HR = 1.13; 95% CI = 0.74–1.71). We observed heterogeneity of effects based on individual-level political affiliation. Among those identifying as Democrats, residing in counties with high (vs. low) levels of polarization appeared to be protective against mortality, with an associated 18% lower risk of dying from all causes (HR = 0.82, 95% CI = 0.71–0.94). This association was strongest in areas with the highest concentrations of Democrats. Conclusions Among all study participants, political group density and polarization at the county level in 2000 were not linked to individual-level mortality. At the same time, we found that Democratic party affiliation may be protective against the adverse effects of high polarization, particularly in counties with high concentrations of Democrats. Future research should further explore these associations to potentially identify new structural interventions to improve population health.