Objective: To (1) validate the Short-Form Health Survey (SF-36) as a generic functional health status measure in patients with rheumatoid arthritis (RA); and (2) assess correlations between the SF-36 and other outcome measures used in the Minocycline in Rheumatoid Arthritis (MIRA) Trial.
Methods: We conducted a cross sectional analysis of the final visit outcome measures from the 48 week, multicenter, placebo controlled, double blind MIRA trial. Multitrait scaling analyses assessed convergent and discriminant validity and internal consistency reliability of the SF-36 in the study patients. Responses to comparable items on the SF-36 and modified Health Assessment Questionnaire (M-HAQ) regarding physical functioning were compared and questions from both instruments were also compared to other RA outcome measures.
Results: In patients with RA, the SF-36 had high internal consistency and reliability, high discriminant and high convergent validity. Moderate correlations were observed (r = -0.46 to -0.61, p < 0.01 in each case) for comparable items on the SF-36 and M-HAQ regarding dressing, walking, and bending. Joint tenderness score correlations with items on the M-HAQ and SF-36, and joint tenderness score correlations with the SF-36 scales were higher than for joint swelling scores. Physician and patient global assessments were most highly correlated (r = 0.58 and 0.66; p < 0.01, respectively) with the SF-36 bodily pain item.
Conclusion: The SF-36 is a valid instrument for this RA population. The SF-36 correlates with the M-HAQ and the physician and patient global assessments. The usefulness of the SF-36 in measuring change in RA clinical trials requires testing in longitudinal studies.