Measuring functional outcomes in chronic disease: a comparison of traditional scales and a self-administered health status questionnaire in patients with rheumatoid arthritis.

A new "health-status" questionnaire, the Sickness Impact Profile (SIP), was examined to determine whether it offered measurement advantages over the traditional American Rheumatism Association (ARA) functional scale or patient self-ratings of function. Seventy-nine outpatients with rheumatoid arthritis (RA) administered the SIP to themselves and provided self-ratings on a 7-point functional scale. Clinicians independently rated patients on the ARA functional scale, and repeated measures were obtained over a 6-month period. Scores on the SIP or its subscales showed stronger correlations than the other scales with hematocrit, sedimentation rate, grip strength, morning stiffness, duration of RA, anatomic stage, work status, and psychiatric status. Validity of the SIP appeared to be maintained with repeated administrations, and the SIP was more reliable than either of the other scales. These findings, as well as the comprehensiveness and feasibility of the self-administered SIP, suggest that this (and perhaps similar health status instruments) may be a useful supplement to more traditional measures of chronic disease outcome.