Association for Public Policy Analysis & Management

Under the Affordable Care Act (ACA), 26 states and Washington D.C. opted to expand their Medicaid programs to cover adults with family income up to 138 percent of the federal poverty threshold during 2014. The potential implications of these expansions for low-income adults could be substantial. Our objective was to assess the preliminary impact of the ACA’s Medicaid expansion on coverage, access to care, and self-reported health using nationally-representative federal survey data.

We used National Health Interview Survey (NHIS) data from 2008-2014 and a difference-in-differences design to compare outcomes for expansion states compared to non-expansion states among non-elderly adults (ages 19-64) with family incomes below the expansion’s eligibility threshold. Outcomes included  insurance coverage, cost-related delays in care, having a usual source of medical care, having seen a general practitioner in the past year, emergency room visits in the past year, flu and tetanus immunization, psychological distress (using the K6 scale), and overall self-reported health. Models adjusted for demographic and economic characteristics, linear and quadratic quarterly time trends, and state fixed effects. 

Low-income adults residing in states that adopted the ACA’s Medicaid expansion were significantly less likely to be uninsured (5.0 percentage point decline, p<0.05) and more likely to have Medicaid coverage (7.2 percentage point increase, p<0.01) in 2014 compared to prior years relative to those in non-expansion states. While the percentage of low-income adults without insurance declined by 1.1 percentage points in non-expansion states, this change was not statistically significant. Private insurance rates increased in non-expansion states (+2.9 percentage points, p<0.05), but the difference-in-difference estimate was not statistically significant.

In addition to changes in coverage, Those residing in expansion states were also significantly less likely to defer care due to cost (2.0 percentage point decline, p<0.05) and report serious psychological distress (3.0 percentage point decline, p<0.10) in 2014 compared to before, though these estimates were not significantly different from the corresponding estimates for non-expansion states. We did not detect a significant change in the likelihood of reporting excellent or good health or in expansion or non-expansion states.

Our findings suggest that the first year of the ACA’s Medicaid expansion was associated with significant gains in insurance coverage and increased health care utilization among low-income adults in expansion compared to non-expansion states. We also found some evidence of increased use of the Emergency Department, perhaps presenting opportunities to ensure that expanded coverage translates into outpatient care where appropriate in 2015 and beyond.