A comparative study of signal versus aggregate methods of outcome measurement based on the WOMAC Osteoarthritis Index. Western Ontario and McMaster Universities Osteoarthritis Index.

Abstract

To compare signal versus aggregate measurement strategies using the VA3.0S version of the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis (OA) Index. Seventy patients with OA of the knee were asked to identify a signal item for each of the 3 dimensions of the WOMAC OA Index at baseline and termination of a 12-week, double blind, randomized, controlled trial. The signal method detected statistically significant alterations in health status at relatively small sample sizes and with a relative efficiency close to or at unity. In addition to a low prevalence of deterioration in nonsignal items, we observed some inconsistency in signal selection. Signal methods of measurement may provide an alternative approach to outcome measurement provided issues of nonsignal deterioration and the consistency of signal selection can be addressed.