Objective: To determine psychometric properties, a cut-off score for severe fatigue and normative data for the 4-item Short Fatigue Questionnaire (SFQ) derived from the multi-dimensional fatigue questionnaire Checklist Individual Strength (CIS).
Methods: Data of previous studies investigating the prevalence of fatigue in ten chronic conditions (n = 2985) and the general population (n = 2288) was used to determine the internal consistency (Cronbach's alpha) of the SFQ, its relation with other fatigue measures (EORTC QLQ-30 fatigue subscale and digital fatigue diary), a cut-off score for severe fatigue (ROC analysis) and to examine whether the four SFQ items truly measure the same construct. Norms were calculated for ten patient groups and the Dutch general population.
Results: Cronbach's alpha of the SFQ were excellent in almost all groups. Pearson's correlations between the SFQ and the EORTC-QLQ-C30 fatigue subscale and a fatigue diary were respectively 0.76 and 0.68. ROC analysis showed an area under the curve of 0.982 (95% CI: 0.979-0.985) and cut-off score of 18 was suggested which showed a good sensitivity (0.984) and specificity (0.826) as well as excellent values for the positive and negative prediction values within all groups using the CIS as golden standard. Factor analysis showed a one factor solution (Eigenvalue: 3.095) with factor loadings of all items on the factor being greater than 0.87.
Conclusion: The SFQ is an easy to use, reliable and valid instrument to screen for severe fatigue in clinical routine and research.
Keywords: Cut-off score.; Psychometrics.; Screening instrument.; Severe fatigue; Short fatigue questionnaire..
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