This report provides a comparison of four national surveys that measure health insurance coverage to asess fundamental methodological issues that impact the variation in health insurance coverage estimates seen among these surveys.  The surveys compared include the Current Population Survey’s Annual Social and Economic Supplement (CPS), the National Health Interview Survey (NHIS), the Survey of Income and Program Participation (SIPP) the Medical Expenditure Panel Survey’s Household Component (MEPS), and six state surveys.   This report was prepared by SHADAC researchers for the U.S. Department of Health and Human Services, Assistant Secretary for Planning and Evaluation (ASPE), and the Agency for Healthcare Research and Quality (AHRQ). November 2007.