Short fatigue questionnaire: screening for severe fatigue, by Adriaan Penson, Sylvia van Deuren, Margreet Worm-Smeitink, Ewald Bronkhorst, Frank HJ van den Hoogen, Baziel GM van Engelen, Marlies Peters, Gijs Bleijenberg, Jan H Vercoulen, Nicole Blijlevens, Eline van Dulmen-den Broeder, Jacqueline Loonen, Hans Knoop in Journal of Psychosomatic Research Vol 137, Oct 2020, 110229 [doi.org/10.1016/j.jpsychores.2020.110229]
- To optimally screen for severe fatigue, a short version of the Checklist Individual Strength was proposed: the Short Fatigue Questionnaire (SFQ)
- Psychometric properties of the SFQ are satisfying
- A cut-off score of 18 is recommended to identify severe fatigue
- Norm values are presented and can be used as reference values
- The SFQ is an excellent instrument to screen for severe fatigue
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).
The Shortened Fatigue Questionnaire (SFQ)  consists of four items (‘I feel tired’, ‘I tire easily‘, ‘I feel fit’ and ‘I feel physically exhausted’; see appendix B). Each item is scored on a 7-point Likert Scale, ranging from 1 ‘yes, that is true’ to 7 ‘no, that is not true’. Scores of items 1, 2 and 4 are reversed and then all item scores are added up which results in a total score varying from 4 to 28. Higher scores reflect a higher level of fatigue.
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.
Cronbach’s alpha of the SFQ were excellent in almost all groups.
Psychometric characteristics of the SFQ were shown to be adequate. Cronbach’s alpha was high for almost all study populations, except for the CFS population. A plausible explanation for the latter could be the fact that the CFS group scored extremely high on the SFQ decreasing the variance of the item- and total scores. The reason why this group scored this high on the SFQ is explained by the fact that one of the criteria to meet the case definition of CFS is scoring above the cut-off score of 35 on the CIS fatigue severity subscale. As the SFQ is derived from the CIS, this will lead to a restricted range of scores. This suggests that the internal consistency itself was not necessarily lower in the CFS population. The relation between the SFQ and other fatigue measures showed the construct validity to be satisfying.
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.
The SFQ is an easy to use, reliable and valid instrument to screen for severe fatigue in clinical routine and research.