Objective. To resolve a conflict in the literature on whether Medicaid-Managed Care (MMC) impacts the Medicaid Undercount.
Data Sources/Study Setting. California county-level data (1995–1997) on MMC penetration, public use data from the Current Population Survey (CPS) (1995–1997), and restricted CPS data matched to administrative records on Medicaid enrollment (2001–2002).
Study Design. We explore the robustness of previous results from the literature first using aggregate data and alternative models. We then examine CPS data linked to Medicaid enrollment data to estimate models of Medicaid reporting errors related to MMC.
Data Collection/Extraction Methods. The Census Bureau linked administrative data on Medicaid enrollment to the CPS. Other data used were public use.
Principal Findings. We find similar results to a previous study using aggregate data that suggest that MMC worsens reporting of Medicaid enrollment. However, using alternative methods we find those results are not statistically significant and can have opposite signs. Our linked CPS microdata analysis suggests that MMC improves reporting. The article concludes with implications of these results for policy makers.
Conclusion. It is unlikely that increased MMC penetration explains the increased Medicaid Undercount.