The SF-36 Health Survey as a generic outcome measure in clinical trials ofpatients with osteoarthritis and rheumatoid arthritis - Relative validity of scales in relation to clinical measures of arthritis severity

OBJECTIVE. TO evaluate the validity of SF-36 Health Survey (SF-36) scale sc ores and summary measure scores to describe the health burden of arthritis and to be responsive to clinical indicators of arthritis severity used in f our clinical trials. METHODS. Adults participating in four double-blinded, placebo-controlled cl inical trials of therapy for osteoarthritis or rheumatoid arthritis were ad ministered the SF-36 concurrent with clinical measures of disease severity (n = 1,016). Data were collected before treatment and 2 weeks after treatme nt. Mean SF-36 scores for all patients with arthritis at baseline were comp ared to a sociodemographically equivalent national norm to test the ability of the SF-36 to describe the burden of arthritis. To test the responsivene ss of SF-36 scores to clinical measures of arthritis severity, mean SF-36 s cale scores were compared across patients differing in arthritis severity b efore treatment. Two-week mean SF-36 change scores were compared across pat ients who improved in arthritis severity (responders) versus patients who d id not improve (nonresponders). F-statistics and relative validity co-effic ients were computed to determine how well each SF-36 scale and summary meas ure discriminated among arthritis severity levels and distinguished treatme nt responders from nonresponders, relative to the best scale. RESULTS. Large and statistically significant differences in mean SF-36 scal e scores and summary measures were found such that trial participants score d in worse health than a sociodemographically equivalent US general populat ion norm. In addition, the largest SF-36 scale scores were found to signifi cantly differ across clinically defined levels of arthritis severity. Final ly, it was found that the SF-36 scales that best discriminate among arthrit is severity groups cross-sectionally were also best at discriminating treat ment responders from nonresponders. CONCLUSION. Results of this study support the validity of the SF-36 to docu ment the health burden of arthritis and as a measure of generic health outc ome for clinical trials of alternative treatments for osteoarthritis and rh eumatoid arthritis patients.