This paper estimates the long-run effects of childhood Medicaid eligibility on adult health and economic outcomes using the program’s original introduction ( 1966–1970) and its mandated coverage of welfare recipients. The design compares cohorts born in different years relative to Medicaid implementation, in states with different preexisting welfare-based eligibility. Early childhood Medicaid eligibility reduces mortality and disability, increases employment, and reduces receipt of disability transfer programs up to 50 years later. Medicaid has saved the government more than its original cost and saved more than 10 million quality adjusted life years.

This paper provides new evidence that Medicaid’s introduction reduced infant and child mortality in the 1960s and 1970s. Mandated coverage of all cash welfare recipients induced substantial cross-state variation in the share of children immediately eligible for the program. Before Medicaid, higher- and lower-eligibility states had similar infant and child mortality trends. After Medicaid, public insurance utilization increased and mortality fell more rapidly among children and infants in high-Medicaid-eligibility states. Mortality among nonwhite children on Medicaid fell by 20 percent, leading to a reduction in aggregate nonwhite child mortality rates of 11 percent.

This paper uses the rollout of the first Community Health Centers (CHCs) to study the longer-term health effects of increasing access to primary care. Within ten years, CHCs are associated with a reduction in age-adjusted mortality rates of 2 percent among those 50 and older. The implied 7 to 13 percent decrease in one-year mortality risk among beneficiaries amounts to 20 to 40 percent of the 1966 poor/non-poor mortality gap for this age group. Large effects for those 65 and older suggest that increased access to primary care has longer-term benefits, even for populations with near universal health insurance.

Covariate-adjusted cross-sectional comparisons show that Medicaid patients have worse health outcomes than other patients. We evaluate the validity of this research design for estimating the causal effect of Medicaid on mortality. Even after controlling for common covariates, Medicaid patients have worse preoperative health and lower socioeconomic status than privately insured patients. Controlling for additional variables shrinks the mortality differences but still does not eliminate imbalance in other predetermined variables. These results can be explained by fairly weak assumptions about unmeasured confounders. We conclude that cross-sectional observational methods do not produce valid causal estimates of Medicaid’s mortality effects.

Difference-in-differences (DiD) is arguably the most popular quasi-experimental research design. Its canonical form, with two groups and two periods, is well understood. However, empirical practices can be ad hoc when researchers go beyond that simple case. This article provides an organizing framework for discussing different types of DiD designs and their associated DiD estimators. It discusses covariates, weights, handling multiple periods, and staggered treatments. The organizational framework, however, applies to other extensions of DiD methods as well.