Medicaid expansion and variability in mortality in the USA: a national, observational cohort study

Summary Background The expansion of the Medicaid public health insurance programme has varied by state in the USA. Longer-term mortality and factors associated with variability in outcomes after Medicaid expansion are under-studied. We aimed to investigate the association of state Medicaid expansion with all-cause mortality. Methods This was a population-based, national, observational cohort study capturing all reported deaths among adults aged 25–64 years via death certificate data in the Centers for Disease Control and Prevention's Wide-ranging Online Data for Epidemiologic Research (CDC WONDER) database in the USA from Jan 1, 2010, to Dec 31, 2018. We obtained national demographic and mortality data for adults aged 25–64 years, and state-level demographics and 2010–18 mortality estimates for the overall population by linking federally maintained registries (CDC WONDER, Behavioral Risk Factor Surveillance System, Health Resources and Services Administration, US Census Bureau, and Bureau of Labor Statistics). States were categorised as Medicaid expansion or non-expansion states as classified by the Kaiser Family Foundation. Multivariable difference-in-differences analysis assessed the absolute difference in the annual, state-level, all-cause mortality per 100 000 adults after Medicaid expansion. Findings Among 32 expansion states and 17 non-expansion states, Medicaid expansion was associated with reductions in all-cause mortality (−11·8 deaths per 100 000 adults [95% CI −21·3 to −2·2]). There was variability in changes in all-cause mortality associated with Medicaid expansion by state (ranging from −63·8 deaths per 100 000 adults [95% CI −134·1 to −42·9] in Delaware to 30·4 deaths per 100 000 adults [–39·8 to 51·4] in New Mexico). State-level proportions of women (−17·8 deaths per 100 000 adults [95% CI −26·7 to −8·8] for each percentage point increase in women residents) and non-Hispanic Black residents (−1·4 deaths per 100 000 adults [–2·4 to −0·3] for each percentage point increase in non-Hispanic Black residents) were associated with greater adjusted reductions in all-cause mortality among expansion states. Interpretation After 4 years of implementation, Medicaid expansion remains associated with significant reductions in all-cause mortality, but reductions are variable by state characteristics. These results could inform policy makers to provide broad-based equitable improvements in health outcomes. Funding University of Southern California Research Center for Liver Diseases.