Khanna D, Pope JE, Khanna PP, Maloney M, Samedi N, Norrie D, Ouimet G, Hays RD. The minimally important difference for the fatigue visual analog scale in patients with rheumatoid arthritis followed in an academic clinical practice.
J Rheumatol 2008;
35:2339-43. [PMID:
19004044 DOI:
10.3899/jrheum.080375]
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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.
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