This paper describes the results of the third phase of a multi-phase research project of University of Minnesota’s State Health Access Data Assistance Center (SHADAC), Centers for Medicare and Medicaid Services (CMS), Assistant Secretary for Planning and Evaluation (ASPE), National Center for Health Statistics (NCHS), and the U.S. Census Bureau. The research is designed to explain why discrepancies exist between survey estimates of enrollment in Medicaid and the number of enrollees reported in state and national administrative data.