This document summarizes a study comparing Medicaid enrollment data from the Medicaid Statistical Information System (MSIS) to survey data from the Current Population Survey (CPS) to understand discrepancies between the two data sources. The study found the CPS significantly undercounted Medicaid enrollment compared to MSIS data. Measurement error in the CPS, particularly issues with question design and sample coverage, appear to contribute most to the undercount. Further analysis is still needed to fully understand and address the differences between the data sources.

1. Fitting Square Pegs Into Round Holes: Linking Medicaid and Current Population Survey Data to Understand the 'Medicaid Undercount' Center’s for Medicare and Medicaid Services Baltimore, MD February 15, 2007 Michael Davern, Ph.D. Assistant Professor, Research Director SHADAC, Health Policy & Management University of Minnesota Supported by a grant from The Robert Wood Johnson Foundation and the Office of the Assistant Secretary for Planning and Evaluation

4. Raw ratios of enrollment counts

5. 0.77- 1.22 0.70 - 0.76 0.62 - 0.69 0.55 - 0.61 0.47 - 0.54 0.36 - 0.46 Adults Ages 0-17 The Current Population Survey Estimate of the Number Enrolled in Medicaid Divided by the Adjusted MSIS Number of Medicaid Enrollees Ages 0-17 2000

6. Number Enrolled in Medicaid Divided by the Adjusted MSIS Number of Medicaid Enrollees 0.84- 1.35 0.77 - 0.83 0.69 - 0.76 0.62 - 0.68 0.54 - 0.61 0.29 - 0.53 Adults Ages 18-64 The Current Population Survey Estimate of the Ages 18-64 2000

7. 0.80- 1.03 0.73 - 0.79 0.65- 0.72 0.58 - 0.64 0.50 - 0.57 0.32 - 0.49 Ages 0-64 The Current Population Survey Estimate of the Number Enrolled in Medicaid Divided by the Adjusted MSIS Number of Medicaid Enrollees Ages 0-64 2000

10. Building a common ‘linked universe’ Group quarters, dead, not a valid ID, in two states Not a valid ID, born In linkable CPS and MSIS universe Medicaid Enrollees in CPS Sample Frame MSIS Medicaid Enrollees

17. How does the CPS compare to other studies of Medicaid reporting error?

22. SHADAC contact information www.shadac.org State Health Access Data Assistance Center University of Minnesota 2221 University Avenue, Suite 345 Minneapolis Minnesota 55414 (612) 624-4802 [email_address]