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OBJECTIVE: To determine the minimal clinically important differences (MCID) in the patient-reported outcomes of activity (0-30, number of days of limitation), fatigue (0 = none, 100 = complete), and sleep quality (0 = no problems, 100 = worst case) for patients with rheumatoid arthritis (RA). METHODS: Two randomized controlled trials comparing abatacept to placebo in RA patients were considered: ATTAIN (n = 391) and AIM (n = 652). An internal anchor-based approach was used to derive the MCID using the Health Assessment Questionnaire, patient global assessment, and pain as anchors. Minimal important change in activity, fatigue, and sleep were determined by estimating mean changes in these outcomes in patients showing change in a narrow range about the MCID of the internal anchor. Correlation analysis was used to determine the consistency of the changes in the outcomes and anchors, and a Delphi process was used to determine the final MCID values. RESULTS: For the 2 trials, consistent patterns of change for activity, fatigue, and sleep and the internal anchors were found with correlations in the range of 0.5, 0.7, and 0.4, respectively. The mean changes for activity, fatigue, and sleep in a narrow range about the MCID of the 3 internal anchors corresponding to the 2 trials were: 3.4 to 4.3 for activity; 6.7 to 17.0 for fatigue; and 4.1 to 7.3 for sleep. Following the Delphi process the MCID determined were 4 for activity, 10 for fatigue, and 6 for sleep. CONCLUSION: These MCID for activity limitation, fatigue, and sleep problems can be used in designing clinical trials and providing benchmarks in assessing patient improvement.