Objective. To determine the discriminant validity of the core set of outcome measures proposed by the American College of Rheumatology (ACR) and the Outcome Measures in Clinical Trials (OMERACT) conference committee to be used in clinical trials of rheumatoid arthritis (RA).
Methods. Utilizing data from a multicenter randomized double-blind clinical trial of low-dose cyclosporine and placebo in RA, we estimated the relative efficiency (RE) of measures to detect a treatment effect (relative to tender joint count, which was assigned a value of 1). Four pain measures (10-cm visual analog scale [VAS], 5-point categorical scale, Health Assessment Questionnaire [HAQ] pain index, Arthritis Impact Measurement Scales [AIMS] pain score) and 3 quality-of-life measures (Problem Elicitation Technique [PET], HAQ, AIMS) were compared.
Results. Physician and patient global measures were the most responsive instruments, although neither was statistically superior to tender joint count. Swollen joint count, grip strength, pain measured on a 10-cm VAS, and functional status as measured by the PET and HAQ were all of intermediate responsiveness. Morning stiffness, 5-point pain scale, and erythrocyte sedimentation rate were the least responsive instruments.
Conclusion. This study provides further evidence to support the core set of outce measures proposed by the ACR and OMERACT.