We used a variety of health status measures in 2 groups of patients with rheumatoid arthritis (RA) to assess both the smallest distinguishable difference and the relative responsiveness to change of these measures, when used in clinical practice.
Two groups of patients were studied. Group 1: 24 patients with stable RA tested on 2 occasions; Group 2: 60 patients receiving methotrexate tested before and 14 weeks after treatment with infliximab. Assessments were made with self-completed questionnaires: the modified Health Assessment Questionnaire, Medical Outcomes Study Short Form-36 [SF-36 (SF-6D)], EuroQol, and, in some, the standard gamble. Group 2 also had joint counts, and measures of erythrocyte sedimentation rate, C-reactive protein, and hemoglobin.
The limits-of-agreement (Bland-Altman) approach had greater confidence intervals (CI) than did CI based on +/- 2 standard errors of the measurement. Improvement with infliximab could be determined with all measures, however, but the standard gamble seemed least responsive to change.
The various measures had different degrees of responsiveness, but with all it was possible to show improvement in Group 2 compared to Group 1. There was a closer association of the patient centered measures of improvement with changes in pain score than with joint counts.