Psychometric Performance of Fatigue Scales in Inflammatory Bowel Disease
Ruth Ann Marrie, John D. Fisk, Casandra Dolovich, Lisa M. Lix, Lesley A. Graff, Scott B. Patten, Çharles N. Bernstein
Abstract
BACKGROUND: Fatigue is highly prevalent in people with inflammatory bowel disease (IBD). Fatigue scales are important for studies testing fatigue interventions, but information about psychometric properties of many scales is insufficient in IBD. We compared the psychometric properties of multiple generic fatigue scales in participants with IBD. METHODS: Individuals with IBD (N = 216) completed the Daily Fatigue Impact Scale (DFIS), the vitality subscale of the RAND-36, and the Patient Health Questionnaire-9 (PHQ-9) fatigue item twice. A subgroup (n = 84) also completed the Fatigue Impact Scale (FIS) once, from which we also scored the 21 items from the Modified Fatigue Impact Scale (MFIS-IBD). We assessed floor/ceiling effects, construct validity, and internal consistency reliability. Using relative efficiency (RE), we compared discriminating ability and comparative responsiveness of the measures regarding disease activity and employment status and changes. RESULTS: The FIS, MFIS, and RAND-36-vitality scales did not exhibit floor or ceiling effects. The DFIS showed mild floor effects (19.4%), and the PHQ-9 fatigue item showed floor (18.1%) and ceiling (20.8%) effects. Internal consistency reliability exceeded 0.93 for FIS, MFIS-IBD, and DFIS and was 0.81 for the RAND-36-vitality scale. In the subgroup analysis, the FIS, MFIS-IBD, and DFIS were strongly correlated with each other (r ≥ 0.90). The ability to discriminate between disease activity groups was highest for the FIS and MFIS-IBD, followed by the DFIS. The FIS, MFIS-IBD, and DFIS were responsive to changes in work impairment. CONCLUSIONS: The FIS, MFIS-IBDs and DFIS had adequate validity and reliability for assessing fatigue in IBD.