Continuous indices of core data set measures in rheumatoid arthritis clinical trials: Lower responses to placebo than seen with categorical responses with the American College of Rheumatology 20% criteria
Article first published online: 7 APR 2005
Copyright © 2005 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 52, Issue 4, pages 1031–1036, April 2005
How to Cite
Pincus, T., Amara, I. and Koch, G. G. (2005), Continuous indices of core data set measures in rheumatoid arthritis clinical trials: Lower responses to placebo than seen with categorical responses with the American College of Rheumatology 20% criteria. Arthritis & Rheumatism, 52: 1031–1036. doi: 10.1002/art.20995
- Issue published online: 7 APR 2005
- Article first published online: 7 APR 2005
- Manuscript Accepted: 29 DEC 2004
- Manuscript Received: 27 MAY 2004
- Arthritis Foundation
- Jack C. Massey Foundation
To describe indices that are continuous counterparts of categorical responses to the American College of Rheumatology 20% improvement criteria (ACR20), ACR50, and ACR70, which extend rheumatoid arthritis (RA) clinical trial results and recognize clinical worsening (as well as improvement) with active and placebo treatments.
Data from a clinical trial of leflunomide, methotrexate, and placebo treatment over 1 year were reanalyzed. Percent change was computed for each of the 7 components of the ACR core set of outcome measures. Four continuous indices were computed: 1) ACR-N (lowest of 3 values: number of swollen joints, number of tender joints, and median of the other 5 measures); 2) composite (median of all 7 measures [3 patient and 3 assessor measures plus erythrocyte sedimentation rate]); 3) patient-only (median of physical function, pain, and global status); and 4) assessor-only (median of number of swollen joints, number of tender joints, and global status). Means, medians, categorical 20%, 50%, and 70% responses, and continuous probability plots were computed according to each index for the 3 treatment groups and were compared with one another and with standard ACR20, ACR50, and ACR70 responses.
Mean levels of improvement calculated using the different methods, in patients taking leflunomide, placebo, and methotrexate, respectively, were as follows: ACR-N 20%, −12%, and 13%; composite 43%, 9%, and 33%; patient-only 36%, 0%, and 26%; assessor-only 50%, 20%, and 44%; and ACR20 52%, 26%, and 46%. Differences between leflunomide and placebo were 30–36%, and differences between methotrexate and placebo were 24–26%.
Continuous indices may be an informative addition to categorical ACR 20%, 50%, or 70% responses to compare efficacies of various treatments in RA, and to describe lower responses to placebo by recognizing worsening as well as improvement.