PAM15: EVALUATING DIRECT AND INDIRECT MEASURES OF UTILITY: STABILITY OF THE SF-6D IN A RHEUMATOID ARTHRITIS POPULATION

Abstract

OBJECTIVES: To evaluate the stability and discriminative ability of direct and indirect measures of utility in a population of rheumatoid arthritis patients. METHODS: Clinical trial data was used to compare the stability of direct measures of utility (SG and VAS) to that from an indirect approach to utility development (SF-6D). SF-36 data were transformed to the SF-6D utility using the algorithm developed by Brazier et al.(1999) based on values of the general UK population. These data were compared to SG and VAS data collected in the same trial. Ability to discriminate across functional classes and variance around point estimates was examined. RESULTS: The SF-6D generated utilities that were consistently lower than the directly elicited SG and were closer to the VAS valuations. The standard deviations, however, were consistently smaller. CONCLUSIONS: The indirect measure of utility (SF-6D) was more stable in terms of variance of parameter estimates and was able to discriminate across functional classes. The reduced variance around these estimates enhances statistical testing and accurately reflects changes experienced by the patient. Baseline Week 24 Week 52 SG 0.7759 (0.2399) 0.8684 (0.1850) 0.8794 (0.1858) VAS 0.5902 (0.1942) 0.7425 (0.1623) 0.7701 (0.1629) SF-6D 0.6287 (0.1290) 0.7323 (0.1109) 0.7443 (0.1089)