Have Past Medicaid Expansions Improved Access to Care for Low-Income Adults?

In January 2014, 26 states will begin implementing the Medicaid expansion allowed by the Affordable Care Act. The expansion is expected to extend coverage to millions of low-income Americans, particularly nonelderly childless adults. Ultimately, the goal is to reduce the financial barriers to obtaining necessary health services and improve health outcomes for this population. We know a great deal from studies of past Medicaid expansions about the effects of extending eligibility on coverage, including the substitution of public for private coverage.  Less is known, however, about the effects of Medicaid expansions on access to and utilization of health care services among low-income adults. Moreover, few studies have focused on expansions to the childless adult population. In this study, we examine the effects of past Medicaid expansions to low-income adults on health care access and use. We separately consider the effects of expansions to parents and childless adults in order to provide more relevant insights with the respect to the impending ACA Medicaid expansion.

We use data from the National Health Interview Survey (NHIS) to measure access and use for nonelderly adults (19-64) over a 15-year period (1997-2011). Access measures include having a usual source of care and having foregone or delayed care due to cost. Utilization measures include having a doctor visit in the past year and having one or multiple emergency department visits in the past year. We compiled information on state Medicaid eligibility rules from a variety of sources and assign eligibility to individuals based on household income, work status, and family structure. Over this period, at least 15 states extended Medicaid eligibility to childless adults and at least 10 states made one or more eligibility expansions to parents. Several states made multiple changes to their eligibility threshold over this period, including restrictions in eligibility. This variation in eligibility thresholds across states and over time is used to identify the effect of Medicaid eligibility on access and use. To address potential endogeneity of Medicaid eligibility, we create a “simulated eligibility” measure by applying each state’s eligibility rules to a fixed random sample of the national population in each year and using the proportion eligible by state and category (i.e., parent, childless adult) as an instrument for individual eligibility. We estimate instrumental variable models to isolate the impact of eligibility on access and use for parents and childless adults.

The results of this analysis will establish the effect of Medicaid eligibility on health care access and use for low-income adults. Importantly, it will measure the net effect of Medicaid eligibility on access and use which will account for any effects on access driven by the substitution of public for private coverage. By focusing on childless adults, this analysis will provide some evidence on the likely effects of expanding eligibility under the ACA. We will also use this analysis to begin assessing the validity of comparison groups for the 26 states that will implement the ACA Medicaid expansion in 2014.