Determination of the minimal clinically important difference for seven fatigue measures in rheumatoid arthritis.
OBJECTIVE
To estimate the minimal clinically important difference (MCID) of seven measures of fatigue in rheumatoid arthritis.


METHODS
A cross-sectional study design based on interindividual 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 partners on a global rating. Ratings were compared to the scores of the fatigue measures to estimate the MCID. Both nonparametric and linear regression analyses were used.


RESULTS
Nonparametric 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: Fatigue Severity Scale, 20.2; Vitality scale of the MOS-SF36, 14.8; Multidimensional Assessment of Fatigue, 18.7; Multidimensional Fatigue Inventory, 16.6; Functional Assessment of Chronic Illness Therapy-Fatigue, 15.9; Chalder Fatigue Scale, 9.9; 10-point numerical Rating Scale, 19.7, for normalized scores (0-100). The standardized MCIDs for the seven measures were roughly similar (0.67-0.76).


CONCLUSIONS
These estimates of MCID will help to interpret changes observed in a fatigue score and will be critical in estimating sample size requirements.
Pouchot
Jacques
J
Arthritis Research Centre of Canada, Division of Rheumatology, University of British Columbia, Vancouver, BC, Canada. jacques.pouchot@egp.aphp.fr
Kherani
Raheem B
RB
Brant
Rollin
R
Lacaille
Diane
D
Lehman
Allen J
AJ
Ensworth
Stephanie
S
Kopec
Jacek
J
Esdaile
John M
JM
Liang
Matthew H
MH
D000368:Aged; D001172:Arthritis, Rheumatoid / Q000150:complications* / Q000523:psychology; D004185:Disability Evaluation; D005221:Fatigue / Q000209:etiology* / Q000523:psychology; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D018434:Sickness Impact Profile