VALUATION OF EUROQOL (EQ-5D) HEALTH STATES IN AN ADULT US SAMPLE

While the EuroQOL instrument (EQ-5D) is being considered and used in c linical trials in the United States and Canada, and in large internati onal multicentre studies, population weights for the instrument have n ever been established in North America. The primary purpose of this in vestigation was to derive a set of US-based population weights for the standard set of health states described in the EQ-5D health questionn aire. Valuations for EQ-5D health states were obtained via a postal su rvey using the visual analogue scale (VAS) format. A sample of 3500 ad ults from the continental US were surveyed. A response rate of 25.8% w as obtained. Mean and median valuations for 45 distinct health states, including dead and unconscious, were calculated. An ordinary least sq uares (OLS) regression-based weighting scheme was constructed to imput e scores for states not directly valued in the questionnaire formats. Valuations for the standard EQ-5D health states displayed similar char acteristics to VAS valuations obtained in previous investigations in E uropean countries. The OLS model fit the observed data relatively well , achieving an adjusted R-2 of 0.42. However, the diagnostic testing i ndicated that the initial model was misspecified. Subsequent alternati ve models alleviated some, but not all, of the problems of misspecific ation. The EQ-5D valuations from adult Americans in this sample appear ed to behave in much the same fashion as in previous valuation studies . However, the generalisability of results to the entire adult America n population may be limited. Violations of assumptions of the OLS regr ession model indicate the need for further investigation into the mode lling technique used in deriving a single index score.