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Blog & News
Recent Publication Round-Up: The 2021 Medicaid Undercount
February 1, 2023:Research has consistently shown that surveys that measure health insurance coverage underestimate the number of people enrolled in Medicaid; this is known as the “Medicaid undercount.” SHADAC researchers have long monitored and investigated the magnitude, causes, and effects of the Medicaid undercount across surveys such as the American Community Survey (ACS) and Current Population Survey Annual Social and Economic Supplement (CPS ASEC) and its prevalence across states and populations.
Two recent SHADAC publications investigate the large increase in the size of the undercount in the 2021 ACS, providing new information and guidance for data users:
The first, “Medicaid Undercount Doubles, Likely Tied to Enrollee Misreporting of Coverage,” describes the large increase in the undercount in the ACS, using longitudinal data from the CPS ASEC to analyze the extent to which the increase in the undercount may be tied to an increase in Medicaid enrollees’ misreporting of coverage due to the pandemic-era Medicaid continuous coverage requirement. |
The second, “Tracking the Medicaid Undercount in the 2021 ACS Coverage Data,” presents state variation in the 2021 ACS’ undercount, how analytic choices such as health insurance coverage hierarchies and misaligned analytic universes (i.e., all persons vs. noninstitutionalized persons) can affect the apparent size of the undercount, and best practices for using 2021 ACS coverage data in light of the increased undercount. |
SHADAC continues to monitor and investigate the Medicaid undercount in surveys of health insurance coverage. The undercount will remain an active area of interest as survey estimates of 2022 health insurance coverage are released later this year and as the “unwinding” of the Medicaid continuous coverage requirement begins this spring.
Publication
Tracking the Medicaid Undercount in the 2021 ACS Coverage Data
Research has consistently shown that health insurance coverage surveys underestimate the number of people enrolled in Medicaid and the extent of this “Medicaid undercount” varies greatly across surveys and states. Among these surveys that measure health insurance coverage, the American Community Survey (ACS) has been shown to have a smaller Medicaid undercount, which is one of the reasons that SHADAC typically relies on this survey to track state-level health insurance coverage.
The “Medicaid undercount” refers to the discrepancies that exist between survey estimates of enrollment in Medicaid and the number of enrollees that are actually reported in state and national administrative data.
With 2021 ACS data being given its normal, official release by the Census Bureau following COVID-19 pandemic-related disruptions, SHADAC is again using the ACS as our primary data source for monitoring state-level health insurance coverage. However, as we and other data users have begun analyzing the 2021 ACS data, it has become apparent that the extent of the ACS’ Medicaid undercount was larger in 2021 than in prior years.
Given the evidence of a greater Medicaid undercount in the 2021 ACS, it is important for users to understand the undercount in the ACS when interpreting coverage estimates. In this brief, we review the research regarding the Medicaid undercount in the ACS, provide estimates of how the undercount varies across states, discuss the impact of assigning single coverage for those with multiple sources on the Medicaid undercount in the ACS, and provide guidance on how to understand health insurance coverage data in the 2021 ACS.
Related SHADAC Resources
Medicaid Undercount Doubles, Likely Tied to Enrollee Misreporting of Coverage (Issue Brief)
Understanding the Undercount of Medicaid Enrollees in the 2020 CPS (SHADAC Blog)
Medicaid Expansion and the Medicaid Undercount in the ACS (Research Article)
Medicaid Undercount Project (Collaborative Study)
Publication
2021 ACS Data: State and County Uninsured Rates, with Comparison Year 2019
Each year, SHADAC uses data released from the American Community Survey (ACS) via the U.S. Census Bureau's data.census.gov tool to produce estimates of uninsurance at the state and county level.*
Click on a state in the interactive map below to view a PDF table of uninsured rates by state and sub-state geographies, but also by demographic characteristics (e.g., age, race/ethnicity, and poverty level) for 2021 and comparison year 2019.^
Click here to view uninsurance estimates for the United States.
Click here to view uninsurance estimates for Puerto Rico and its municipios.
Note: These tables present uninsured rates, which indicate the share of the population that is uninsured. For example, a 10 percent uninsured rate for adult women indicates that 10 percent of all adult women are uninsured.
Additional Estimates (50-State Comparisons)
Maps & Tables of Private, Public, & Uninsured Changes from 2019 to 2021
Private Coverage Rates by State, Change from 2019 to 2021, for All People
Public Coverage Rates by State, Change from 2019 to 2021, for All People
Uninsurance Rates by State, Change from 2019 to 2021, for All People
Uninsurance Rates by State, Change from 2019 to 2021, for Children under age 18
About the ACS
The ACS is a household survey that began in 2005 and produces annually updated data on a variety of population characteristics, including health insurance coverage. In total, the ACS surveys approximately three million U.S. households each year. An important feature of the ACS is that it includes a large enough sample for state‐level and sub‐state estimates.
The ACS began asking survey respondents about health insurance coverage during the 2008 calendar year. Specifically, the survey asks respondents about current coverage for each person in the respondent’s household. A person is categorized as “insured” if he or she has coverage at the point in time at which the survey is administered.
*Why Aren’t Estimates Provided for All Counties?
Due to sample size constraints, single-year ACS estimates are available at the county level only for counties with a population greater than 65,000.
^Why Are the Estimates Being Compared to 2019 and not to 2020?
Impacts of the COVID-19 pandemic on survey data collection and dissemination efforts, as well as the presence of measurable nonresponse bias, resulted in ACS estimates from data year 2020 being released on an “experimental only” basis, and the Census Bureau has recommended that these estimates not be used or compared to any other data year.
How Are These Estimates Different from the Estimates that SHADAC Publishes Using Census Bureau Micro-Data Files?
Two definitions used by the Census Bureau to generate the tabulations above differ from those that SHADAC uses to generate tabulations for State Health Compare. The definitional differences are as follows:
Family
The Census Bureau defines a family as “all related people in a household.”
SHADAC defines a family using a measure called the “Health Insurance Unit” (HIU), which includes all individuals who would likely be considered a family unit in determining eligibility for either private or public coverage.
To learn more about the 2020 update of SHADAC's Health Insurance Unit (HIU) see our HIU resource page, which houses two issue briefs: The first describes the SHADAC HIU, its purpose, the most recent update, and improvements to HIU data inputs; and the second outlines the impacts of using the SHADAC HIU in analysis so that researchers can assess whether the SHADAC HIU is suitable for their research and what the potential impacts of its use might be. The page also provides a link to STATA and SAS codes to aid in the use of the HIU variable.
Family Income
The Census Bureau determines family income as a percentage of the Federal Poverty Level (FPL), which is a definition of poverty used primarily for statistical purposes. For example, FPL is used to estimate the number of Americans living in poverty each year.
SHADAC determines family income as a percentage of the U.S. Department of Health and Human Services’ Federal Poverty Guideline (FPG), which is a measure used for administrative purposes. For example, FPG is used to determine eligibility for federal programs such as Medicaid and the Supplemental Nutrition Assistance Program (SNAP).
Check out our blog post from May 2022 to learn more about the difference between FPL and FPG,
Related ACS Materials:
Publication
Medicaid Undercount Doubles, Likely Tied to Enrollee Misreporting of Coverage
Medicaid and Children’s Health Insurance Plan (CHIP) programs have played a key role in responding to the COVID-19 pandemic, providing an important safety net for health insurance coverage for millions of people during this unprecedented public health crisis. The Families First Coronavirus Response Act enacted the continuous coverage requirement, which provides a 6.2 percentage point increase in federal matching funds for states that maintain continuous Medicaid enrollment until the end of the public health emergency. Subsequently, administrative records show that enrollment in Medicaid and CHIP has grown substantially.
However, key federal surveys such as the American Community Survey have failed to show the extent of this growth in the population with Medicaid/CHIP coverage. This brief describes our analysis of these estimates, focused on the size of the “Medicaid undercount”, the misalignment between survey estimates of self-reported Medicaid coverage, and enrollment counts obtained from Medicaid/CHIP administrative data.
The Medicaid undercount in the 2021 American Community Survey (ACS) was larger than in earlier years, which we believe was tied, at least in part, to the Medicaid continuous coverage requirement. In the brief, we also present analysis of two years of linked data from the Current Population Survey Annual Social and Economic and Supplement (CPS ASEC). Our results suggest that despite having continuous coverage, many enrollees may not have known they were still covered by Medicaid.
Related Resources
Blog & News
Key Resources and 2022 Updates: SHADAC's Health Insurance Unit
October 2022:Updated April 2023
In the years following the passage of the Patient Protection and Affordable Care Act (ACA), SHADAC developed and introduced its Health Insurance Unit, or “HIU,” a tool to aid in defining family interrelationships in federal population surveys for the purpose of analyzing health insurance coverage.
Since the inception of this tool, SHADAC has regularly produced updated HIU variables, including in fall 2022 following the release of the 2021 American Community Survey (ACS) and 2022 Current Population Survey Annual Social and Economic Supplement (CPS ASEC). These variables were recently made available via IPUMS-CPS (October 19, 2022) and IPUMS-USA (March 10, 2023). These HIU variables use the updated HIU methodology introduced in 2020 and incorporate the latest years of survey data and federal poverty guidelines, as relevant.
What is the SHADAC HIU?
First released in 2012, one of the goals of the SHADAC HIU is to establish a common definition of a “family unit” to help ensure consistent and comparative research across major national surveys when analyzing health insurance coverage.
Most federal surveys define a “family” differently from the way it is defined by most private and public insurance programs. For instance, the definition of "family" or "household" in U.S. Census Bureau surveys includes all related members of a household, no matter the degree of relationship, and does not necessarily align with dependent coverage or public program eligibility.
The SHADAC HIU attempts to more closely align with a definition of family used for private and public health insurance coverage eligibility. The SHADAC HIU uses a narrower definition of family that looks at specific interrelationships between individuals within a household and excludes all non-dependent relatives (grandparents, adult siblings, aunts/uncles, etc.) who may be household members but are unlikely to be considered as part of the “family unit” as defined for the purposes of determining eligibility for health insurance.
The SHADAC HIU, then, is defined as an economic unit that consists of those members of a household who would likely be eligible as a group for family health insurance coverage, or whose resources (i.e., income) would be considered in determining eligibility for public coverage.
Related Resources
- Defining Family for Studies of Health Insurance Coverage (August 2021): A brief that outlines the impacts of using the SHADAC HIU in analysis—specifically, analysis showing how the population distribution of family income changes using three different definitions of family: all members in the same household (Census definition), the definition used by the IPUMS (described below), and the SHADAC HIU (described in detail in a companion brief). Researchers can use this brief to assess whether the SHADAC HIU is suitable for their analysis and what the potential impacts of its use might be.
- Stata Code (January 2021): Technical documentation of statistical code in STATA to help researchers to employ the SHADAC HIU in their own analysis using ACS microdata downloaded from IPUMS USA.
