Criteria for improvement in rheumatoid arthritis: alternatives to the American College of Rheumatology 20.

Objective: Appropriate outcome measures are critical to estimating treatment effects in clinical trials and observational studies. The American College of Rheumatology 20 (ACR 20) is the standard measure to assess treatment effects in rheumatoid arthritis (RA) randomized controlled clinical trials (RCT). Although the ACR 20, which measures at least a 20% improvement in a number of different measures, is a very useful dichotomous measure for identifying novel treatments with potential activity, it may fail to discriminate among active treatments.