Joint effects of US area-level social mobility & income inequality on mortality: an ecological study

Abstract

Abstract Background Income inequality and its relationship with health has been extensively studied. Intergenerational income mobility (IGIM) has received less attention, but may be an important independent mechanism explaining health inequalities. Methods We conducted ecological analyses of the effects of IGIM and income inequality on mortality across commuting zones (CZ) in the US. IGIM was measured using rank-rank slope, i.e. the correlation between household income rank at age 15-19 and own income rank at age 29-30. We used CZ-level IGIM data from the Opportunity Insights project, Gini index of inequality from the American Community Survey, and mortality rates from CDC WONDER. Cross-sectional and longitudinal (CZ fixed effects) regression models were fitted adjusting for mean income and weighted by population. Results CZs with higher IGIM between 1995-2001 and 2011-12 had lower age-standardised mortality in 2009-2013, with 53.9 (95% CI: 48.9-58.9) fewer deaths per 100,000 for a standard deviation (SD) increase in IGIM (adjusting for mean income and Gini index in 2009-2013). This equates to 778 (773-783) deaths at the lower quartile vs. 710 (705-715) at the upper. Income inequality had a negligible association at 1.1 (-5.0, 7.3) deaths per SD increase. Longitudinal analysis across three 5-year periods confirmed that within-CZ changes in infant mortality were predicted by changes in IGIM (32.0 [12.7-51.2] fewer deaths per SD increase) but not income inequality (4.5 [-12.0, 20.9] deaths per SD increase). Conclusions Preliminary evidence suggests IGIM is a more important indicator for population health than income inequality. European researchers and public health bodies should further research and monitor IGIM, which may require improved availability of intergenerationally linked income data. Policy measures that improve social mobility, such as education and early-years interventions, may have greater health effects than policies only aiming at resource redistribution. Key messages • Differences in intergenerational income mobility accounted for substantial differences in mortality across US commuting zones, while income inequality appeared relatively unimportant. • European policymakers should put greater emphasis on social mobility as an economic determinant of health, and facilitate research using intergenerationally linked income data.