The SIPP estimates are ERIU tabulations of data collected by the U.S. Census Bureau in the Survey of Income and Program Participation (SIPP) 2001 panel, which began in January 2001. The SIPP interviews respondents every four months over a period of roughly 4 years. The 2001 tabulations are based on responses to the first three interviews (waves) of the 2001 panel, covering a 12-month period that corresponds with calendar year 2001 for one of the four rotation groups. Respondents report whether they were covered by specific sources of public or private health insurance (Medicare, Medicaid, SCHIP, other public, employment-based private, other private health insurance). Respondents are considered uninsured if they respond “no” to all of the coverage options; they are not asked directly if they are uninsured. Respondents are considered uninsured if they respond “no” to all of the coverage options; they are not asked directly if they are uninsured. The “point in time” estimate reflects health insurance status in the 12th survey month. The “all year uninsured” estimate includes those without health insurance for all 12 months. The “ever uninsured” includes those reporting no health insurance for at least one month and for as many as 12 months.

For further discussion of issues related to counting the uninsured see "Counting and Characterizing the Uninsured," (Adobe PDF) by Pamela Farley Short, and ERIU Research Highlight 1: A Revolving Door: How Individuals Move In and Out of Health Insurance Coverage (Adobe PDF)

Notes on SIPP Data Source and Variables (PDF)