This report is released to inform interested parties of health insurance coverage research and to encourage discussion.

The Current Population Survey (CPS) Annual Social and Economic Supplement (ASEC) and the Survey of Income and Program Participation (SIPP) are commonly used data sets for health insurance coverage estimates. Although both surveys are household surveys conducted by the United States Census Bureau, they are designed to meet different needs and, hence, have different sample sizes, interview techniques, sample compositions, and survey reference periods. Accordingly, the two surveys produce varying health insurance coverage rates.

The CPS ASEC, which collects annual information, found that 83.6 percent of people were covered by health insurance for some or all of 1998. The SIPP, which collects monthly information, found 92.0 percent of people covered by health insurance for at least 1 month of 1998. Since the SIPP collects monthly information and allows us to see changes from month to month, SIPP may be closer to the truth. This implies that although designed to estimate the coverage at some point during a year, the CPS is underestimating it. Some researchers believe that the CPS estimates are closer to point-in-time estimates than the annual estimate in the SIPP.