This paper describes the results of the fifth phase of a multi-phase research project coordinated by the 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), Administration for Healthcare Research and Quality (AHRQ), and 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.