Abstract
Objective
To estimate the minimally important difference (MID) for a fatigue visual analog scale (VAS) using patient-reported anchors (fatigue, pain, and overall health).
Methods
Patients with rheumatoid arthritis (RA; n = 307) had 2 clinic visits at a median of 5.9 months apart. They completed a fatigue VAS (0–10 scale) and the retrospective anchor items, “How would you describe your overall fatigue/pain/overall health since the last visit?” with response options: Much worsened, Somewhat worsened, Same, Somewhat better, or Much better. The fatigue anchor was used for primary analysis and the pain/overall health anchors for sensitivity analyses. The minimally changed group was defined by those reporting they were somewhat better or somewhat worsened.
Results
The mean [standard deviation (SD)] age was 59.4 (13.2) years, disease duration was 14.1 (11.5) years, and 83% of patients were women. The baseline mean (SD) Health Assessment Questionnaire–Disability Index score was 0.84 (0.75). The baseline fatigue VAS score was 4.2 (2.9) and at followup was 4.3 (2.8) [mean change of −0.07 (2.5); p = not significant]. The fatigue change score (0–10 scale) for Somewhat better and Somewhat worsened for the fatigue anchor averaged −1.12 and 1.26, respectively. Using the pain anchor, the fatigue change score for Somewhat better and Somewhat worsened averaged −0.87 and 1.13; and using the global anchor, the fatigue change score for Somewhat better and Somewhat worsened averaged −0.82 and 1.17, respectively. Effect size estimates using 3 anchors were small for the Somewhat better (range 0.27–0.39) and Somewhat worsened (0.40–0.44) groups, but larger than for the no-change group (0.03–0.08).
Conclusion
The MID for fatigue VAS is between −0.82 for −1.12 for improvement and is 1.13 to 1.26 for worsening on a 0–10 scale in a large RA clinical practice, and is similar to that seen in RA clinical trials. This information can aid in interpreting fatigue VAS in day-to-day care in clinical practice
Key Indexing Terms:Footnotes
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D. Khanna, MD, MS, Assistant Professor of Medicine, Division of Rheumatology, Department of Medicine, David Geffen School of Medicine, UCLA, and Department of Health Services, School of Public Health, UCLA; J.E. Pope, MD, MPH, FRCPC, Professor of Medicine, Division of Rheumatology, St. Joseph’s Health Care and University of Western Ontario; P.P. Khanna, MD, MPH, Fellow in Rheumatology, Division of Rheumatology, Department of Medicine, David Geffen School of Medicine, UCLA; M. Maloney, BA, MA, Medical Student; N. Samedi, MD, Resident in Rheumatology; D. Norrie, BSc, MD, Resident, Division of Rheumatology, St. Joseph’s Health Care and University of Western Ontario; G. Ouimet, BSc, Research Assistant, Division of Rheumatology, St. Joseph’s Health Care; R.D. Hays, PhD, Professor of Medicine, Division of Rheumatology, Department of Medicine, David Geffen School of Medicine and Department of Health Services, School of Public Health, UCLA, and Rand Corporation, Santa Monica, CA.
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Dr. D. Khanna was supported by a National Institutes of Health Award (NIAMS K23 AR053858-01A1). Dr. P.P. Khanna was supported by a National Institutes of Health Award (T32 AR 053463). Dr. Hays was supported by the UCLA Center for Health Improvement in Minority Elderly/Resource Centers for Minority Aging Research, NIH/NIA/NCMHD, under Grant 2P30-AG-021684 and a grant from the National Institute on Aging (AG 020679-01). Pfizer Inc. and Bristol- Meyer Squibs Inc. provided unrestricted grants for portions of the study.
- Accepted for publication July 14, 2008.
