Validating the SF-36 health survey questionnaire in patients with psoriatic arthritis

Objective. To assess the reliability and validity of the SF-36 in patients with psoriatic arthritis (PsA). Methods. The SF-36 was administered to all patients attending the University of Toronto Psoriatic Arthritis Clinic between January and December 1994. Clinical and radiological assessments were performed during the clinic visits. Results. We studied 113 patients, 43 women and 70 men, with a mean age of 50.5 years and a mean arthritis duration of 14.2 years. The reliability of the SF-36 was high, with the Cronbach alpha coefficient exceeding 0.90 for all the 8 health scales. The SF-36 was able to detect meaningful differences in health status between patients with PsA and individuals from the general population. As predicted, patients with PsA reported substantially lower scores on the physical functioning, role limitations due to physical problems, and pain scales. They also reported significantly lower scores on the role limitations due to emotional problems and general health perception scale, In general all scales were moderately to highly correlated with measures of function and pain (r=0.33-0.67), while the physical functioning, pain, and vitality scales were also moderately correlated with disease activity (r=0.34-0.42). With one exception the scales were unrelated to disease severity. Conclusion. The SF-36 questionnaire is reliable and valid for use in PsA, supporting its use as an adjunct outcome measure for clinical trials in PsA. Because the SF-36 can be used to compare health status across different patient populations, its application can also help to clarify the disease burden associated with PsA.