The Affordable Care Act (ACA) gives states the option of expanding Medicaid coverage to individuals and families with incomes of up to 138 percent of the federal poverty level. A new study, being released today as a Web First by Health Affairs, used simulation methods to compare nondisabled adults enrolled in Medicaid before the ACA with newly eligible adults and those previously eligible but not enrolled in the program.

According to the study’s analysis, both the newly eligible and those not previously enrolled were healthier than the pre-ACA Medicaid enrollees. Authors Steven Hill, Salam Abdus, Julie Hudson, and Thomas Selden found that the pattern of results was similar for physical and mental health. They also determined that in states not expanding Medicaid under the ACA, adults in the income range for the law’s Medicaid expansion were healthier than pre-ACA enrollees.

The authors used simulation methods and data from the Medical Expenditure Panel Survey (MEPS). To obtain larger samples, they pooled data from six years, 2005–2010, reporting “point in time” insurance and eligibility at the first interview in each calendar year. “Our findings could have implications for the likely degree of adverse selection among newly eligible adults,” concluded the authors.

They also found that “before the ACA, Medicaid experienced only modest adverse selection: Enrollees were less healthy than people who were eligible but not enrolled,” although the differences, “while statistically significant, were not large.”

Looking at the twenty-five states that so far have opted out of Medicaid expansion, the authors observed that “if these states reverse their decisions, their Medicaid programs might be likely to enroll a population that is healthier than their pre-ACA enrollees. By electing to expand Medicaid eligibility, states could provide coverage to millions of healthier adults as well as to millions who have chronic conditions and who need care.”

Hill, Hudson, and Selden are affiliated with the Center for Financing, Access, and Cost Trends at the Agency for Healthcare Research and Quality (AHRQ in Rockville, Maryland); Abdus is a senior economist at Social and Scientific Systems, in Rockville. The study will also appear in the April issue of Health Affairs.