This report prepared by the State Health Access Data Assistance Center (SHADAC) explores how using new data from the American Community Survey could complement existing Census data to estimate the number of uninsured Americans at the county level.

From the briefing:

Misreporting of uninsurance by Medicaid enrollees is a major concern for policy‐makers. Misreporting can impact uninsurance estimates in two ways: those with insurance may falsely report they are uninsured and those without insurance may mistakenly report they have insurance.

In comparison to administrative data, most surveys undercount the number of people thought to be enrolled in Medicaid. Researchers speculate that this could be due to a variety of factors such as underreporting of Medicaid coverage due to social stigma, lack of awareness of enrollment, or confusion about the type of coverage respondents have (e.g., Medicare or Medicaid). The extent to which uninsurance estimates are overestimated varies by the reference period – the longer the recall period, the more likely a known Medicaid enrollee will erroneously say they are uninsured. The CPS, with its long reference period, demonstrates the Survey Uninsured for the Entire Year Uninsured at a Specific Point-in-Time most significant amount of recall error with Medicaid enrollees reporting as uninsured. Surveys using point-in‐time measures of coverage result in modest upward bias to uninsurance estimates.

Full briefing: Comparing Federal Government Surveys that Count Uninsured People in America (PDF | 298.81 KB)

Robert Wood Johnson Foundation (2009). Comparing federal government surveys that count uninsured people in America.