Unequal spillover of human capital: longitudinal analysis of mortality among populations by college degree in U.S. counties, 2010-2022.

Introduction: County-level educational attainment is known to affect mortality rates, but little is understood about how these effects differ between populations with and without a bachelor's degree (BA). This study examined the association between county-level human capital and mortality rates of populations with and without a BA in U.S. counties, and how it changed between 2010 and 2022.

Methods: Assembling 2010-2022 data of 3,122 counties (40,585 county-year observations), this study used fixed-effect negative binomial regression to analyze mortality rates stratified by educational attainment. Mortality data came from the National Center for Health Statistics Multiple Cause of Death files and county-level human capital was measured as percentage of population aged 25 and over with a BA. County-level demographic, economic, and health-related factors were considered in the analysis conducted in 2024.

Results: County-level human capital showed divergent effects. A 1% increase in county BA population corresponded to a 4.5% decrease in all-cause mortality for those with a BA but a 1.2% increase for those without a BA. Over the study period, this disparity moderated, primarily due to a weakening protective effect among BA holders in high-human capital counties. This pattern persists across other causes of death.

Conclusions: The benefits of living in highly educated areas are not uniformly distributed, potentially exacerbating health inequalities. While county-level human capital remains protective for those with a BA, this advantage has diminished over time, while the adverse effect on those without a BA has stabilized.