Abstract
The Functional Assessment of Cancer Therapy–Fatigue (FACIT-Fatigue) is a well-validated instrument to assess fatigue in cancer or other chronic illnesses. It can be reported as a single global fatigue score (GFS) or as separate scores for symptoms (FSS) and impacts (FIS) (Cella, 2011). Confirmatory factor analysis (CFA) and bifactor analysis were conducted to evaluate if this dimensionality also holds in the CLL population. FACIT-Fatigue data from 263 CLL patients were analyzed. Single factor models were specified for GFS, FSS and FIS to determine the dimensionality of all 13 items of FACIT-Fatigue. A bifactor model was tested including a global factor (defined by loadings of all 13 items) and two subdomain factors: symptoms (5 items) and impacts (8 items). Criteria of a Root Mean Square Error of Approximation (RMSEA) <0.10 and a Comparative Fit Index (CFI) >0.90 were set to define acceptable model fit. Mean scores for the items ranged from 0.53 to 2.23 (item range 0-4). For the three single-factor models specified (GFS, FSS and FIS), CFI values were >0.90 and RMSEA <0.10. All item factor loadings were statistically significant and >0.3. Bifactor model fit was excellent (CFI>0.95; RMSEA<0.08). All items had higher loadings on GFS, ranging from 0.36 (“Able to do my usual activities”) to 0.92 (“Trouble starting things”), than on their sub-domain factors, supporting the essential unidimensionality of the FACIT-Fatigue. Conclusion: Results confirmed the findings of Cella (2011) in the CLL population. FACIT-Fatigue is unidimensional, and the GFS is a valid endpoint to report in clinical research. If preferred by researchers, it can also be supplemented with two definable components of fatigue, symptoms and impacts, as supported by the bifactor model and CFA results for each subdomain. Being able to distinguish between these components enhances understanding of patients’ experience in CLL.
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