Determination of the minimal clinically important difference for seven fatigue measures in rheumatoid arthritis

Abstract

Objective-To estimate the minimal clinically important difference (MCID) of seven measures of fatigue in rheumatoid arthritis.Study Design and Setting-A cross-sectional study design based on inter-individual comparisons was used. Six to eight subjects participated in a single meeting and completed seven fatigue questionnaires (nine sessions were organized and 61 subjects participated). After completion of the questionnaires, the subjects had five one-on-one 10-minute conversations with different people in the group to discuss their fatigue. After each conversation, each patient compared their fatigue to their conversational partner's on a global rating. Ratings were compared to the scores of the fatigue measures to estimate the MCID. Both non-parametric and linear regression analyses were used.Results-Non-parametric estimates for the MCID relative to "little more fatigue" tended to be smaller than those for "little less fatigue". The global MCIDs estimated by linear regression were: FSS 20.2, VT 14.8, MAF 18.7, MFI 16.6, CFS 9.9, RS 19.7, for normalized scores (0 to 100). The standardized MCIDs for the seven measures were roughly similar (0.67 to 0.76). Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Fatigue is a non-specific subjective symptom. In the absence of an objective measurement, fatigue can only be assessed by asking the subject. The measurement properties of available instruments need to be evaluated if they are to be used clinically or in clinical trials. Among the psychometric properties, longitudinal validity (responsiveness, sensitivity to change) is one of the most important. Closely related is the minimal clinically important difference (MCID), which is defined as "the smallest difference in score in the domain of interest (fatigue) which patients perceive as beneficial and which would mandate, in the absence of troublesome side effects and excessive cost, a change in the patient's management" [9]. The MCID is essential to interpret the magnitude of longitudinal changes or differences when comparing two treatments or different group of patients. Knowledge of MCID is also essential for meaningful sample size calculations in clinical trials. NIH Public AccessThe aim of our study was to estimate the MCID of seven validated self-administered measures of fatigue in persons with RA. The fatigue instruments identified from a literature review as suitable for use in RA and studied were: the Fatigue Severity Scale (FSS) [10,11] Patients and Methods PatientsThe study was conducted at the Mary Pack Arthritis Centre, Vancouver, Canada. All participants signe...

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