Association of Social Mobility With the Income-Related Longevity Gap in the United States: A Cross-Sectional, County-Level Study

IMPORTANCE: Despite substantial research, the drivers of the widening gap in life expectancy between rich and poor individuals in the United States—known as the longevity gap—remain unknown. The hypothesis of this study is that social mobility may play an important role in explaining the longevity gap. OBJECTIVE: To assess whether social mobility is associated with income-related differences in life expectancy in the United States. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional, ecological study used data from 1559 counties in the United States to assess the association of social mobility with average life expectancy at age 40 years by sex and income quartile among adult men and women over the period of January 2000 through December 2014. Bayesian generalized linear multilevel regression models were used to estimate the association, with adjustment for a range of socioeconomic, demographic, and health care system characteristics. EXPOSURES: County-level social mobility, here operationalized as the association of the income rank of individuals born during the period of January 1980 through December 1982 (based on tax record data, averaged over the period January 2010 through December 2012) with the income ranks of their parents (averaged over the period January 1996 through December 2000) using the location where the parent first claimed the child as a dependent at age 15 years to identify counties. MAIN OUTCOMES AND MEASURES: The main outcome was life expectancy at age 40 years by sex and income quartile. RESULTS: The sample consisted of 1559 counties, which represented 93% of the US population in 2000. Each 1-SD increase in social mobility—equivalent to the difference between a low-mobility state, such as Alabama (ranked 49th on this measure), and a higher-mobility state, such as Massachusetts (ranked 23rd on this measure)—was associated with a 0.38-year (95% credible interval [CrI], 0.29-0.47) and a 0.29-year (95% CrI, 0.21-0.38) increase in county-level life expectancy among men and women, respectively, in the lowest income quartile. Estimates for life expectancies among county residents in the highest income quartile were smaller in magnitude and not robust to covariate adjustment (men: 0.10-year [95% CrI, −0.02 to 0.22] increase; women: 0.08-year [95% CrI, −0.05 to 0.20] increase). Increasing social mobility in all counties to the value of the highest social mobility county was associated with decreases in the life expectancy gap between the highest and lowest income quartiles by 1.4 (95% CrI, 0.7-2.1) years for men and 1.1 (95% CrI, 0.5-1.6) years for women nationally, representing a 20% decrease. CONCLUSIONS AND RELEVANCE: In this cross-sectional study, higher county-level social mobility was associated with smaller county-level gaps in life expectancy by income. These findings motivate further investigation of causal relationships between policies that shift social mobility and health outcomes.