Objective: To evaluate the capacity of a pooled index of only the 3 patient self-report questionnaire measures among the 7 American College of Rheumatology (ACR) core data set (Core Data Set) measures to distinguish efficacy of active treatment of rheumatoid arthritis (RA) with leflunomide or methotrexate versus placebo in a randomized, controlled clinical trial, and to compare the results with those obtained using the ACR 20% response criteria (ACR20), Disease Activity Score (DAS), and other pooled indices.
Methods: The 7 ACR Core Data Set measures of 1) joint swelling, 2) joint tenderness, 3) physician global assessment, 4) erythrocyte sedimentation rate (ESR), 5) functional disability, 6) pain, and 7) patient global assessment were combined into the following 5 pooled indices: "All Core Data Set" (all 7 measures), "Assessor Only" (measures 1-3), "Assessor + ESR" (measures 1-4), "Patient Only" (measures 5-7), and "Patient + ESR" (measures 4-7). The capacity of each of these 5 indices to detect differences between active treatment and placebo treatment was compared with that of the ACR20 and the DAS using 4 different analytic methods, each of which presented advantages and limitations. Agreement of the indices with one another and with the ACR20 and the DAS was analyzed according to pairwise kappa statistics and Z scores in multivariate logistic regression models.
Results: Each of the 5 indices, including "Patient Only," had a similar capacity to detect greater efficacy of leflunomide and methotrexate versus placebo in this clinical trial, according to each of 4 methods, at similar levels of statistical and clinical significance.
Conclusion: A pooled index of patient self-report questionnaire Core Data Set measures appears to be as informative as ACR20 responses, DAS scores, and pooled indices of all and assessor-derived Core Data Set measures for distinguishing between active treatment and placebo treatment in this RA clinical trial.