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Article Excerpt
Survey estimates of public program enrollment are substantially lower than estimates of program enrollment compiled from administrative data for Medicaid, Temporary Assistance for Needy Families, and Food Stamps (C. Taeuber, D. Resnick, S. Love, J. Staveley, P. Wilde, and R. Larson, unpublished data; Lynch et al. 2007; Call et al. 2008). This discordance is particularly apparent for Medicaid and has become known as the "Medicaid undercount" (Lewis, Elwood, and Czajka 1998; Klerman, Ringel, and Roth 2005; Call et al. 2008; Davern et al. 2008). The crude Medicaid undercount in the 2001 Current Population Survey (CPS)'s Annual Social and Economic Supplement (ASEC) was 42 percent, corresponding to calendar year 2000; in the 2002 CPS it was 43 percent, corresponding to calendar year 2001. (1)
This large Medicaid undercount in the CPS is particularly problematic because the CPS is widely used for official and unofficial health policy research purposes at the national and state level (Blewett et al. 2004). At the national level, CPS estimates are used by statute in the allocation of State Children's Health Insurance Program (SCHIP) funds to states (Davern et al. 2003). In addition, the Congressional Budget Office uses CPS-based estimates to "score" (i.e., estimate the cost of) legislation (Glied, Remler, and Zivin 2002). The CPS data are also used by state health policy analysts to examine the potential cost and impact of state-level health reform legislation and to report to the federal government on their progress toward insuring low-income uninsured children through SCHIP and other efforts (Blewett and Davern 2006). Unofficially the CPS is widely used by the academic and policy research community to evaluate health policy reforms and to estimate policy-relevant populations within each state, such as the number of people who are eligible for but not enrolled in public health insurance coverage (Blewett et al. 2004).
These uses of the CPS data emphasize the importance of an improved understanding of the Medicaid undercount in the CPS. Toward this end, this paper reports preliminary results from a project that linked MSIS Medicaid enrollment data to CPS survey data. The U.S. Census Bureau constructed files and performed tabulations that allow us to break the undercount into two components: (1) MSIS counts of people outside the CPS sampling frame and (2) survey response errors among those in the CPS sample. The resulting analysis presented in this paper provides insight into the contributions of these two components of the undercount, although an exact accounting is still not possible.
DATA, METHODS, AND ANALYSIS PLAN
Our analysis uses the 2000-2002 Medicaid Statistical Information System (MSIS) data from the Centers for Medicare and Medicaid Services (CMS), the 2001 and 2002 CPS (2) survey data (reporting on health insurance coverage in calendar years 2000 and 2001), and linking procedures of the Census Bureau.
The Survey Data
The CPS is a monthly household survey of noninstitutional dwelling units. Its primary purpose is to generate the official monthly estimates of the unemployment rate. Individuals residing within selected dwelling units are interviewed according to a rolling panel design--the same four consecutive months in two successive calendar years. Interviews are primarily conducted in person in the first month that a dwelling unit is in the sample and via telephone or in person thereafter. Proxy responses are allowed; one member of the household generally responds for the entire household (U.S. Census Bureau 2002a).
While this monthly CPS survey only collects information sufficient to estimate the unemployment rate, the ASEC appends to the monthly CPS household interview detailed questions about income, employment, and program participation during the previous calendar year. Most of the ASEC interviews occur in March with some additional interviews occurring in February and April (U.S. Census Bureau 2002a; Davern et al. 2003). The 2001 and 2002 ASECs that we analyze here both had response rates of 84 percent (U.S. Census Bureau 2002b, 2003).
Since 1980, the ASEC has included a module on health insurance coverage. Consistent with the reference period for the income and labor force questions in the ASEC, the health insurance questions (including the Medicaid question) refer to the entire previous calendar year. This is in contrast to most other surveys that collect information on health insurance at the time of the interview (some also ask about coverage during the past year as well).
The basic ASEC health insurance question is structured to ask the household respondent if s/he or anyone else in the household had one of several different types of insurance coverage at any point during the last year. After ascertaining that a specific type of coverage is operative for the household, a follow-up question is asked about who else in the household was enrolled. The specific types of health insurance coverage included in the household level screen portion of the interview are as follows: an employer or union plan; self-purchased insurance; someone outside the home provides coverage for anyone in the home; Medicare; Medicaid; SCHIP, other state-specific public health insurance programs; an item combining the VA, Military Health Care, and Indian Health Service; and a final "other" insurance please specify. (3) For any individual in the household with no affirmative answer for any of these types of health insurance, the household respondent is asked an uninsurance verification question: "I have recorded that (READ NAMES) were not covered by a health plan at any time in YEAR. Is that correct?" For both the "other" type of coverage and the verification question, a follow-up question for affirmative response allows the respondent to choose from the fifteen types of coverage (of which Medicaid is a possible answer).
In our analysis, we code all Medicaid responses as being "reported Medicaid" whether the Medicaid response came from the verification question, the "other public" health insurance question, or the Medicaid-specific survey item itself. However, the person needed to respond "Medicaid" or the state program name for Medicaid and not something else (e.g., SCHIP) to be included. We code all other types of coverage, including SCHIP, as other (non-Medicaid) types of health insurance coverage.
The Administrative Data
The MSIS data include an eligibility record for each individual enrolled in Medicaid. The Balanced Budget Act of 1997 mandated that states submit detailed individual-level Medicaid enrollment data to CMS. States are required to prepare data in a format specified by CMS; the data are then edited and cleaned by a CMS contractor and anomalies are noted in an appendix on the CMS website (CMS 2007a). Detailed information about the data element requirements is available from MSIS Tape Specification and Data Dictionary (CMS 2007b). For each recorded person, the MSIS data include the number of days enrolled by month, as well as various descriptors of coverage status and type. For our research, we use the 2000-2002 calendar year MSIS data files. Consistent with the CPS reference period, we count anyone who the MSIS indicated was enrolled with full-benefit Medicaid or enrolled in restricted Medicaid benefits for pregnancy services (4) for at least 1 day in the CPS calendar year reference period as having "full-benefit Medicaid" coverage (calendar years 2000 and 2001). People enrolled during the year in SCHIP only and not Medicaid in the MSIS are not considered "full-benefit Medicaid" enrollees. We did this because SCHIP is not consistently submitted by the states for inclusion into the MSIS.
Linking the Administrative and Survey Data
For this project, CMS provided the Census Bureau with a version of its MSIS files for 2000-2002 that included an SSN. Within its secure data analysis facilities, the Census Bureau validated the SSN on the MSIS file and replaced the validated SSNs on the MSIS...
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