Assessing measurement error in Medicare coverage from the National Health Interview Survey.

Objectives: Using linked administrative data, to validate Medicare coverage estimates among adults aged 65 or older from the National Health Interview Survey (NHIS), and to assess the impact of a recently added Medicare probe question on the validity of these estimates.

Data sources: Linked 2005 NHIS and Master Beneficiary Record and Payment History Update System files from the Social Security Administration (SSA).

Study design: We compared Medicare coverage reported on NHIS with "benchmark" benefit records from SSA.

Principal findings: With the addition of the probe question, more reports of coverage were captured, and the agreement between the NHIS-reported coverage and SSA records increased from 88% to 95%. Few additional overreports were observed.

Conclusions: Increased accuracy of the Medicare coverage status of NHIS participants was achieved with the Medicare probe question. Though some misclassification remains, data users interested in Medicare coverage as an outcome or correlate can use this survey measure with confidence.