Medicaid currently insures 60 million people, and the Affordable Care Act (ACA) will extend Medicaid eligibility to millions more starting in 2014. The recent Supreme Court ruling enables states to choose whether to expand Medicaid under the ACA, and many states facing budget pressures are considering cutbacks instead. Yet evidence regarding Medicaid's effect on health remains surprisingly sparse, particularly for adults. Previous research showed that Medicaid expansions in the 1980s reduced mortality among infants and children, though other studies showed little effect. Numerous observational studies have documented a correlation between Medicaid coverage and adverse outcomes among adults prompting some observers to claim that Medicaid coverage is worse than no coverage. However, such studies are plagued by unmeasured confounders that make Medicaid patients sicker than others. One ongoing randomized trial of an expansion of Medicaid in Oregon showed significant improvements in self-reported health and access to care in the first year.

Traditionally, Medicaid covers only low-income children, parents, pregnant women, and disabled persons. During the past decade, however, several states have expanded Medicaid to cover nondisabled adults without dependent children (“childless adults”), a group that is similar to the population gaining eligibility under the ACA (i.e., all adults with incomes up to 138% of the federal poverty level). We used this natural experiment to determine whether state expansions of Medicaid were associated with decreased mortality. We hypothesized that Medicaid expansions would reduce mortality, rates of uninsurance, and cost-related barriers to care and would improve self-reported health, particularly among minority and lower-income populations. (author abstract)