Report for Phase I of the Medicaid Undercount Project (SNACC). This phase involved creating a national database of health-insurance enrollment and evaluate the quality of the information it contains. This was done by merging the CMS Medicaid Statistical Information System (MSIS) files with the CMS Medicare (EDB) files. The quality of the database of health-insurance enrollment was evaluated by assessing the ability to accurately merge the input files and by comparing the characteristics of the individuals in the database to expectations based on Medicaid eligibility rules and characteristics of the U.S. population. February 2007.