Content Validity and Psychometric Evaluation of the Functional Assessment of Chronic Illness Therapy–Fatigue (FACIT–Fatigue) in Patients with Crohn’s Disease and Ulcerative Colitis

Background: Patients with Crohn’s disease (CD) or ulcerative colitis (UC) frequently experience fatigue, although it is often overlooked in medical research and practice. Aims: To explore patients’ experience of fatigue and evaluate content validity, psychometric properties, and score interpretability of the Functional Assessment of Chronic Illness Therapy–Fatigue (FACIT–Fatigue) in patients with CD or UC. Methods: Concept elicitation and cognitive interviews were conducted with participants aged ≥ 15 years with moderately-to-severely active CD (N = 30) or UC (N = 33). To evaluate psychometric properties (reliability and construct validity) and interpretation of FACIT–Fatigue scores, data from two clinical trials were analyzed [ADVANCE (CD): N = 850; U-ACHIEVE (UC): 248]. Meaningful within-person change was estimated using anchor-based methods. Results: Almost all interview participants reported experiencing fatigue. Over 30 unique fatigue-related impacts were reported per condition. The FACIT–Fatigue was interpretable for most patients. FACIT–Fatigue items had good internal consistency (Cronbach’s α 0.86–0.88 for CD and 0.94–0.96 for UC); the total score displayed acceptable test–retest reliability (intraclass correlation coefficients > 0.60 for CD and > 0.90 for UC). FACIT–Fatigue scores had acceptable convergent validity with similar measures. A 7–10 point improvement for CD and 4–9 point improvement for UC on the FACIT–Fatigue total score may represent meaningful improvements. Conclusions: These results highlight the importance of fatigue among adolescents and adults with CD or UC and provide evidence that the FACIT–Fatigue is content valid and produces reliable, valid, and interpretable scores in these populations. Care should be taken if using the questionnaire with adolescents who may be less familiar with the word “fatigue.” Clinical trial registration numbers NCT03105128 (date of registration: 4 April 2017) and NCT02819635 (date of registration: 28 June 2016).