Performance of the Norwegian SF-36 Health Survey in patients with rheumatoid arthritis. II. A comparison of the SF-36 with disease-specific measures.

The performance of the SF-36 was compared with disease-specific health status instruments (Arthritis Impact Measurements Scales [AIMS2], Modified Health Assessment Questionnaire [MHAQ] and visual analogue scales) in 1030 patients with rheumatoid arthritis (mean age 62.3 years, 79% females, mean disease duration 12.9 years, 48% rheumatoid factor positive). The scales performed similarly in known group comparisons (age cohorts, disease severity, disease activity, comorbidity). The SF-36 physical functioning scale correlated -0.69 and -0.73 with the MHAQ and AIMS2 physical scales, respectively. A strong negative correlation was found with the walking and bending subscale of AIMS2 (r = -0.80), a substantial negative correlation with mobility (r = -0.65), and moderate correlations with the scales for hand/finger and arm function (r = -0.52 and r = -0.53). Frequency distributions of scores revealed more skewed distributions of the AIMS2 physical scale and the MHAQ scale than the physical functioning scale of the SF36, whereas the pain and mental health scales were distributed similarly. In conclusion, the SF-36 performs well in patients with rheumatoid arthritis. The physical functioning scale of the SF-36 does not seem to capture all aspects of physical health in rheumatoid arthritis patients, but may be more sensitive than disease-specific measures to low levels of physical disability.