An arthritis-specific health index (ASHI) for the SF-36 Health Survey was developed by studying its responsiveness to changes in clinical indicators of arthritis severity. Longitudinal data from 1,076 patients participating in four placebo-controlled trials were analyzed. All had at least a 6-month history of moderate to severe osteoarthritis or rheumatoid arthritis of the knee or hip. All had undergone a washout period of 3 to 14 days before baseline assessment to bring about a flare state in osteoarthritis or rheumatoid arthritis symptoms. Their average age was 60 years and 72% were female. Change scores for the eight-scale SF-36 health profile (acute version) and five arthritis-specific measures of disease severity (knee pain on weight bearing, time to walk 50 feet, physician global evaluation of symptom severity and impact, patient global evaluation of symptom severity and impact, and pain intensity visual analogue scale) were computed by subtracting scores before treatment from scores at two-week follow-up. Canonical correlation methods were used to derive weights for changes in SF-36 scales to score a single index (ASHI) that maximized its correlation with changes in the set of five clinical measures of arthritis severity. The weights used to score the ASHI were cross-validated in a 25% holdout group (N = 144) from the first two osteoarthritis trials and in two additional osteoarthritis and rheumatoid arthritis trials (N = 530). Only one SF-36 canonical variate (ASHI) correlated significantly (F = 4.69, P < 0.0001) with the clinical canonical variate that served as the "criterion" measure of change in the severity of arthritis. Changes in the ASHI and clinical canonical variate were substantially correlated in the developmental sample (r = 0.628, P < 0.0001) and on cross-validation (r = 0.629, P < 0.0001). The clinical canonical variate correlated highly (r = 0.75-0.88) with changes in all but one of the five clinical measures (50-foot walk; r = 0.41). The pattern of correlations between changes in SF-36 scales and the ASHI indicated that ASHI is primarily a measure of bodily pain (r = 0.92) and other aspects of physical and role functioning and well-being (r = 0.69 for Role-Physical, r = 0.68 for Physical Functioning, r = 0.52 for Social Functioning, and r = 0.51 Vitality). The patterns of correlations between SF-36 scales and the ASHI were very similar across developmental and cross-validation samples. This research demonstrates the feasibility and generalizability of a single ASHI scored from changes in responses to the SF-36 Health Survey. The generic SF-36 health profile, which has already been shown to be useful in comparing arthritis with other diseases and treatments, can also be scored specifically to make it more useful in studies of osteoarthritis and rheumatoid arthritis.

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.

OBJECTIVE: The SF-36 Arthritis-Specific Health Index (ASHI) was constructed to improve the responsiveness of the SF-36 Health Survey to changes in the severity of arthritis through the use of arthritis-specific scoring algorithms. This study compared the responsiveness of the ASHI and other generic scales and summary measures scored from the SF-36 in clinical trials of health outcomes for patients with arthritis. METHODS: Longitudinal data for patients (n = 835) participating in four placebo-controlled trials were analyzed. Study participants had at least a 6-month history of moderate to severe osteoarthritis or rheumatoid arthritis of the knee or hip. All had undergone a washout period of 3 to 14 days before baseline assessment to bring about a flare state in osteoarthritis or rheumatoid arthritis symptoms. Their average age was 60 years, and 72% were female. Responders and nonresponders were classified on the basis of physician assessments of changes in arthritis severity, with blinding as to treatment group; treated and untreated (placebo) groups were also compared. For the SF-36 ASHI, generic physical (PCS) and mental (MCS) component summary measures and each of eight subscales scored from the SF-36 (acute version) change scores were computed by subtracting scores before treatment from scores at 2-week follow-up. To evaluate empirical validity, analyses of variance were performed. For each measure, an F-ratio was computed for the comparison between clinically defined groups of responders and nonresponders and between groups of patients assigned to placebo versus drug therapy. Relative validity (RV) coefficients were computed for the ASHI in comparison with PCS, MCS, and the best SF-36 scale to determine which was more responsive. RESULTS: In analyses of each of the four trials and all trials combined, RV coefficients for the ASHI were higher than those for both of the generic SF-36 summary measures and for the most valid SF-36 scale (Bodily Pain), with only one exception. Across 40 tests of validity in distinguishing treated from untreated patients, the ASHI was 5% to 19% more valid than the best SF-36 scale (RV = 1.05-1.19; RV = 1.10 in all trials combined). The generic summary measures (PCS and MCS) were much less valid in these tests (RV = 0.67 and 0.27, respectively). In analyses of responders and nonresponders, RV coefficients for the ASHI ranged from 0.70 to 1.22 (RV = 1.04 in all trials combined), in comparison with the best SF-36 subscale, which was always Bodily Pain. RV coefficients were lower for PCS (RV = 0.75) and much lower than the MCS (RV = 0.18) in comparisons of treatment outcomes based on all trials combined. CONCLUSION: The ASHI appears to be more valid than the eight SF-36 scales and PCS and MCS summary measures for purposes of distinguishing between treated and untreated patients and between clinical responders and nonresponders. This study demonstrates the feasibility of improving the validity of the SF-36 through the use of arthritis-specific scoring while retaining the option of generic scoring, which makes it possible to also compare results across diseases and treatments.

OBJECTIVE: To evaluate the psychometric assumptions underlying the construction and scoring of SF-36 scales and summary measures among clinical trial participants with arthritis. METHODS: Cross-sectional SF-36 data from the baseline assessment of adult patients (n = 1,016) participating in four placebo-controlled clinical trials of treatment for arthritis were analyzed with blinding as to treatment. Tests of the completeness of data, scaling assumptions, internal-consistency reliability, and factor structure of SF-36 scales were performed for the combined sample. Eligible participants had at least a 6-month history of moderate to severe osteoarthritis or rheumatoid arthritis of the knee or hip. Participants meeting inclusion criteria had undergone a washout period of 3-14 days before baseline assessment to bring about a flare state in osteoarthritis or rheumatoid arthritis symptoms. Baseline sample sizes for the three osteoarthritis trials were n = 121, n = 341, and n = 187. The baseline sample size for the rheumatoid arthritis trial was n = 367. The average age of participants was 60 years, and the majority were females (72%). Measured were functional health and well-being scales and physical and mental health summary measures from the SF-36 Health Survey acute form. RESULTS: Missing responses ranged from 0.0% to 1.5% across SF-36 items, and scale scores could be computed for 96.8% to 100% of participants across trials. In all four trials, item internal consistency tests were passed (91.4%-97.1%) and item discriminant validity tests were passed (96.9%-100.0%). Across the four trials, internal-consistency reliability coefficients ranged from a low of 0.75 to a high of 0.91 for the eight scales (median = 0.84), exceeding the minimum standards for group comparisons. Ceiling effects were minimal for most scales, and floor effects were noteworthy for the role physical and role emotional scales. Physical and mental health factors identified in previous studies were replicated. CONCLUSION: The SF-36 Health Survey proved to be a psychometrically sound tool for the assessment of the health status of adult participants in clinical trials of arthritis.