Comparison of Medicare claims versus physician adjudication for identifying stroke outcomes in the Women's Health Initiative.

ABSTRACT

BACKGROUND AND PURPOSE: Many studies use medical record review for ascertaining outcomes. One large, longitudinal study, the Women's Health Initiative (WHI), ascertains strokes using participant self-report and subsequent physician review of medical records. This is resource-intensive. Herein, we assess whether Medicare data can reliably assess stroke events in the WHI. METHODS: Subjects were WHI participants with fee-for-service Medicare. Four stroke definitions were created for Medicare data using discharge diagnoses in hospitalization claims: definition 1, stroke codes in any position; definition 2, primary position stroke codes; and definitions 3 and 4, hemorrhagic and ischemic stroke codes, respectively. WHI data were randomly split into training (50%) and test sets. A concordance matrix was used to examine the agreement between WHI and Medicare stroke diagnosis. A WHI stroke and a Medicare stroke were considered a match if they occurred within ±7 days of each other. Refined analyses excluded Medicare events when medical records were unavailable for comparison. RESULTS: Training data consisted of 24 428 randomly selected participants. There were 577 WHI strokes and 557 Medicare strokes using definition 1. Of these, 478 were a match. With regard to algorithm performance, specificity was 99.7%, negative predictive value was 99.7%, sensitivity was 82.8%, positive predictive value was 85.8%, and κ=0.84. Performance was similar for test data. Whereas specificity and negative predictive value exceeded 99%, sensitivity ranged from 75% to 88% and positive predictive value ranged from 80% to 90% across stroke definitions. CONCLUSIONS: Medicare data seem useful for population-based stroke research; however, performance characteristics depend on the definition selected.