The SF-36 Health Survey as a generic outcome measure in clinical trials of patients 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 scores and summary measure scores to describe the health burden of arthritis and to be responsive to clinical indicators of arthritis severity used in four clinical trials.

METHODS

Adults participating in four double-blinded, placebo-controlled clinical trials of therapy for osteoarthritis or rheumatoid arthritis were administered the SF-36 concurrent with clinical measures of disease severity (n = 1,016). Data were collected before treatment and 2 weeks after treatment. Mean SF-36 scores for all patients with arthritis at baseline were compared to a sociodemographically equivalent national norm to test the ability of the SF-36 to describe the burden of arthritis. To test the responsiveness of SF-36 scores to clinical measures of arthritis severity, mean SF-36 scale scores were compared across patients differing in arthritis severity before treatment. Two-week mean SF-36 change scores were compared across patients who improved in arthritis severity (responders) versus patients who did not improve (nonresponders). F-statistics and relative validity coefficients were computed to determine how well each SF-36 scale and summary measure discriminated among arthritis severity levels and distinguished treatment responders from nonresponders, relative to the best scale.

RESULTS

Large and statistically significant differences in mean SF-36 scale scores and summary measures were found such that trial participants scored in worse health than a sociodemographically equivalent US general population norm. In addition, the largest SF-36 scale scores were found to significantly differ across clinically defined levels of arthritis severity. Finally, it was found that the SF-36 scales that best discriminate among arthritis severity groups cross-sectionally were also best at discriminating treatment responders from nonresponders.

CONCLUSION

Results of this study support the validity of the SF-36 to document the health burden of arthritis and as a measure of generic health outcome for clinical trials of alternative treatments for osteoarthritis and rheumatoid arthritis patients.