The Coverage Gap: Uninsured Poor Adults in States that Do Not Expand Medicaid

This analysis uses data from the 2019 American Community Survey (ACS). The ACS provides socioeconomic and demographic information for the United States population and specific subpopulations. Importantly, the ACS provides detailed data on families and households, which we use to determine income and household composition for ACA eligibility purposes.

Medicaid and Marketplaces have different rules about household composition and income for eligibility. The ACS questionnaire captures the relationship between each household resident and one household reference person, but not necessarily each individual to all others. Therefore, prior to estimating eligibility, we implement a series of logical rules based on each person’s relationship to that household reference person in order to estimate the person-to-person relationships of all individuals within a respondent household to one another. We then assess income eligibility for both Medicaid and Marketplace subsidies by grouping individuals into household insurance units (HIUs) and calculate HIU income using the rules for each program. For more detail on how we construct person-to-person relationships, aggregate Medicaid and Marketplace households, and then count income, see the detailed Technical Appendix A.

Undocumented immigrants are ineligible for federally-funded Medicaid and Marketplace coverage. Since ACS data do not directly indicate whether an immigrant is lawfully present, we draw on the methods underlying the 2013 analysis by the State Health Access Data Assistance Center (SHADAC) and the recommendations made by Van Hook et. Al.1,2 This approach uses the Survey of Income and Program Participation (SIPP) to develop a model that predicts immigration status; it then applies the model to ACS, controlling to state-level estimates of total undocumented population from Pew Research Center. For more detail on the immigration imputation used in this analysis, see the Technical Appendix B.

Individuals in tax-filing units with access to an affordable offer of Employer-Sponsored Insurance (ESI) are still potentially MAGI-eligible for Medicaid coverage, but they are ineligible for advance premium tax credits in the Health Insurance Exchanges. Since ACS data do not designate policyholders of employment-based coverage nor indicate whether workers hold an offer of ESI, we developed a model that predicts both the policyholder and the offer of ESI based on the Current Population Survey (CPS). Additionally, for families with a Marketplace eligibility level below 250% FPL, we assume any reported worker offer does not meet affordability requirements and therefore does not disqualify the family from Tax Credit eligibility on the Exchanges. For more detail on the offer imputation used in this analysis, see the Technical Appendix C.

As of January 2014, Medicaid financial eligibility for most nonelderly adults is based on modified adjusted gross income (MAGI). To determine whether each individual is eligible for Medicaid, we use each state’s reported eligibility levels as of January 1, 2020, updated to reflect state Medicaid expansion decisions as of November 2020 and 2020 Federal Poverty Levels.3 Some nonelderly adults with incomes above MAGI levels may be eligible for Medicaid through other pathways; however, we only assess eligibility through the MAGI pathway.4

An individual’s income is likely to fluctuate throughout the year, impacting his or her eligibility for Medicaid. Our estimates are based on annual income and thus represent a snapshot of the number of people in the coverage gap at a given point in time. Over the course of the year, a larger number of people are likely to move and out of the coverage gap as their income fluctuates.

Starting with our of estimates of ACA eligibility in 2017, we transferred our core modeling approach from relying on the Current Population Survey (CPS) Annual Social and Economic Supplement (ASEC) to the American Community Survey (ACS). ACS includes a 1% sample of the US population and allows for precise state-level estimates as well as longer trend analyses. Since our methodology excludes a small number of individuals whose poverty status could not be determined, our ACS-based population totals appear slightly below CPS-based totals and some ACS population totals published by the Census Bureau. This difference is in large part attributable to students who reside in college dormitories. Comparing the two survey designs, CPS counts more of these individuals in the household of their parent(s) than ACS does.

Issue Brief Technical Appendix A: Household Construction

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