A Closer Look at the Remaining Uninsured Population Eligible for Medicaid and CHIP

This analysis uses data from the 2015 Current Population Survey (CPS) Annual Social and Economic Supplement (ASEC). The CPS ASEC provides socioeconomic and demographic information for the United States population and specific subpopulations. Importantly, the CPS ASEC provides detailed data on families and households, which we use to determine income for ACA eligibility purposes.

The CPS asks respondents about coverage at the time of the interview (for the 2015 CPS, February, March, or April 2015) as well as throughout the preceding calendar year. People who report any type of coverage throughout the preceding calendar year are counted as “insured.” Thus, the calendar year measure of the uninsured population captures people who lacked coverage for the entirety of 2014 (and thus were uninsured at the start of 2015). We use this measure of insurance coverage, rather than the measure of coverage at the time of interview, because the latter lacks detail about coverage type that is used in our model. Based on other survey data, as well as administrative data on ACA enrollment, it is likely that a small number of people included in this analysis gained coverage in 2015.

Medicaid and Marketplaces have different rules about household composition and income for eligibility. For this analysis, we calculate household membership and income for both Medicaid and Marketplace premium tax credits for each person individually, using the rules for each program. For more detail on how we construct Medicaid and Marketplace households and count income, see the detailed technical Appendix A available here.

Undocumented immigrants are ineligible for Medicaid and Marketplace coverage. Since CPS 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 CPS, controlling to state-level estimates of total undocumented population from Department of Homeland Security. For more detail on the immigration imputation used in this analysis, see the technical Appendix B available here.

Individuals in tax-filing units with access to an affordable offer of Employer-Sponsored Insurance are still potentially MAGI-eligible for Medicaid coverage, but they are ineligible for advance premium tax credits in the Health Insurance Exchanges. Since CPS data do not directly indicate whether workers have access to ESI, we draw on the methods comparable to our imputation of authorization status and use SIPP to develop a model that predicts offer of ESI, then apply the model to CPS. For more detail on the offer imputation used in this analysis, see the technical Appendix C available here.

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, 2015, updated to reflect state implementation of the Medicaid expansion as of January 2016 and 2015 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.

Issue Brief

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