In states that expanded Medicaid eligibility under the Affordable Care Act, nonelderly near-poor adults-those with family incomes of 100-138 percent of the federal poverty level-are generally eligible for Medicaid, with no premiums and minimal cost sharing. In states that did not expand eligibility, these adults may qualify for premium tax credits to purchase Marketplace plans that have out-of-pocket premiums and cost-sharing requirements. We used data for 2010-15 to estimate the effects of Medicaid expansion on coverage and out-of-pocket expenses, compared to the effects of Marketplace coverage. For adults with family incomes of 100-138 percent of poverty, living in a Medicaid expansion state was associated with a 4.5-percentage-point reduction in the probability of being uninsured, a $344 decline in average total out-of-pocket spending, a 4.1-percentage-point decline in high out-of-pocket spending burden (that is, spending more than 10 percent of income), and a 7.7-percentage-point decline in the probability of having any out-of-pocket spending relative to living in a nonexpansion state. These findings suggest that policies that substitute Marketplace for Medicaid eligibility could lower coverage rates and increase out-of-pocket expenses for enrollees.

The significant gains in health insurance coverage and improvements in health care access and affordability that followed the implementation of the key coverage provisions of the Affordable Care Act in 2014 have persisted into 2017. Adults in all parts of the country, of all ages, and across all income groups have benefited from a large and sustained increase in the percentage of the US population that has health insurance. The gains have been particularly striking among low- and moderate-income Americans living in states that expanded Medicaid. Our latest survey data from the Urban Institute's 2017 Health Reform Monitoring Survey shows that only 10.2 percent of nonelderly adults are now uninsured-a decline of almost 41 percent from the period before implementation of the ACA. Nonetheless, repealing and replacing the ACA remained under consideration during the summer of 2017, along with more systematic changes to the financing of the Medicaid program. Many people will be at substantial risk if key components of the law are repealed or otherwise changed without carefully considering the health and financial consequences for those projected to lose coverage. Though the politics of health reform are challenging, opportunities exist to create a more equitable and efficient health care system.

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The Affordable Care Act (ACA) made private nongroup health insurance more accessible to nonelderly adults with chronic conditions, with enrollment growth occurring through the federal and state-based Marketplaces. During the July through December reference period in 2014-15, 45 percent of Marketplace enrollees ages 18-64 were treated for chronic conditions, compared with 35 percent of non-Marketplace nongroup enrollees and 38 percent of adults with employer-sponsored insurance. Marketplace enrollees also had higher service use than other privately insured adults did, which likely contributed to rising premiums in the nongroup market. As repeal of the ACA individual mandate takes effect in 2019, protecting coverage gains for adults with chronic conditions while stabilizing nongroup premiums may depend on state-level efforts to spread the risk of Marketplace enrollees' health care costs across a balanced insurance pool.

In 2015, adults likely to have enrolled in the Affordable Care Act Marketplace were predominantly non-Hispanic whites and, on average, older and more aware of the availability of Marketplace subsidies than adults who remained uninsured. Enrollees were also significantly more likely than adults who remained uninsured to rely on some type of application assistance instead of exclusively looking for information through the Marketplace website.