The Impact of the Affordable Care Act Medicaid Expansion on Insurance Status and Type of Coverage for Non-Disabled Childless Adults in Poverty

We use data from the 2009-2014 National Health Interview Survey (NHIS) with restricted-access state geocodes to estimate the effect of the Affordable Care Act’s (ACA’s) Medicaid expansion  on insurance status and type of coverage for adults who became newly eligible for Medicaid in 2014. Our differences-in-differences research design exploits policy variation created by state decisions to opt out of Medicaid expansion. In addition to using a gold-standard federal survey with reliable identification of insurance type, we contribute to the literature by focusing on non-disabled childless adults in poverty (9 million people nationwide in 2014), a segment of the expansion's target population who lacked pre-2014 eligibility for Medicaid in the 14 expansion states we study. By carefully defining the population of interest, we are able to estimate how Medicaid expansion affected insurance enrollment among non-disabled childless adults in poverty relative to a control group of similar adults in non-expansion states who  were not targeted by other ACA-related coverage expansions. These design choices allow us to interpret our estimates in terms of marginal take-up by the newly eligible, whereas differences-in-differences estimates that define the treatment group to include all adults covered by the ACA Medicaid expansion in all expansion states may overestimate the effect of expansion due to  woodwork effects (i.e., take-up among previously eligible adults).

We find that expanding Medicaid to non-disabled childless adults in poverty reduced uninsurance among this group by 14.9 percentage points (35.5% of the 2013 uninsurance rate) in states where they were previously ineligible compared to observably similar adults in non-expansion states. This decrease in uninsurance was driven primarily by a 15.4 percentage point increase in Medicaid coverage. Our estimates of the marginal take-up rate are substantially higher than is typical in the literature, suggesting that administrative changes in enrollment, response to the individual mandate, and public awareness of the ACA may have led to higher take-up than usual. The 2014 Medicaid expansion had no impact on private insurance coverage in our population of interest, suggesting that "crowd-out" of private coverage was limited in 2014. These findings are robust to controls for differential pre-ACA trends in coverage in expansion and non-expansion states.

In subgroup analyses, we find that men in the target population were eight percentage points less likely than women to gain insurance coverage, and that this gender difference was driven entirely by differences in Medicaid take-up. We also found dramatically higher Medicaid take-up among adults over age 35 (by 10-20 percentage points) relative to younger  adults, and among those in fair or poor health (by 19 percentage points) relative to healthier adults.

These findings suggest that the ACA’s Medicaid expansion successfully increased the number of insured individuals, and that those with the greatest health need (e.g. older adults, those in fair or poor health) were most likely to take-up coverage in response to the expansion. Further, we find no evidence of crowd-out of employer coverage among this population, implying that—at least in 2014—expanding Medicaid to low-income childless adults effectively targeted previously uninsured individuals.