Original articleMeasuring fatigue in clinical and community settings
Introduction
Fatigue after exertion is normal although an excessive level of fatigability is often related to a variety of chronic conditions. Fatigue is considered the most severe and debilitating symptom in chronic fatigue syndrome (CFS) [1]. CFS patients present with persistent and relapsing unexplained fatigue with new and definitive onset lasting for at least 6 months. The prevalence of CFS is estimated between 0.1% and 3% in the general population depending upon the diagnostic criteria used [2], [3]. CFS is associated with significant disability in personal and professional settings [4]. It is estimated that only 5% (i.e., median full recovery rate) of the CFS patients will naturally recover [5]; a number of treatments including cognitive behavioral therapy and graded exercise therapy have shown to be effective in reducing fatigue [6]. Reliable quantification and detection of abnormal levels of fatigue in both general and clinical populations are therefore important to formulate early intervention plans and to assess effectiveness of treatments.
In 1993, Chalder et al. [7] developed a 14-item scale to measure fatigue. In this study, the newly developed scale was administered to new registrations at a general practice. Following a principal component analysis (PCA) and item discriminative properties based on receiver-operating characteristic (ROC) analysis, the authors excluded three items proposing a final scale of 11 items [7]. Principal component analysis resulted in two components, namely, physical and mental fatigue. Since its introduction, the Chalder Fatigue Scale (CFQ) has been used in a variety of settings including randomized controlled trials [8], general population [9], primary and secondary care [8], [9], [10]. The scale has also been used in measuring fatigue in various conditions including cancer [11], postpolio syndrome [12], and multiple sclerosis [13].
Morriss et al. [14] examined the reliability of the scale in CFS patients finding that four factors denoted fatigue. Factors found were cognitive difficulties (I), tiredness and sleepiness (II), strength and endurance (III), and loss of interest and motivation (IV). In this study, the authors retained all the components with eigenvalues higher than 1, according to Kaiser's retention rule [15]. As a result, Component IV included only two items, one of which (Item 6) had a higher loading on Component I. Similarly, Components II and III had higher loadings for Item 9. In discussing the results of the PCA, the authors noted that the patients used for the analysis were part of a randomized controlled trial and therefore may not have been representative of CFS patients. Due to these limitations and to the lack of clear definition in the components identified, a replication of the factorial structure of the fatigue scale seems warranted.
Despite its large use, no study has attempted to cross-validate the psychometric property of the fatigue scale comparing clinical and nonclinical populations. This would allow testing of the discriminative properties of the scale (i.e., sensitivity and specificity) and would inform about the ability to differentiate between clinical and nonclinical fatigue at different levels.
Section snippets
Participants
For this study, 361 CFS patients in secondary care and 1615 participants in the community were recruited.
CFS patients were recruited from consecutive referrals to the Chronic Fatigue Unit at the South London and Maudsley NHS Trust. The clinic provides a specialized multidisciplinary assessment and treatment service to CFS patients across the southeast of England. The patients included in this study were referred from primary care, assessed by a doctor at the clinic, and were diagnosed with CFS.
Results
The CFS group had a mean age of 39.1 (S.D. 10.8), while the community sample had a mean age of 34 (S.D. 7.6). Gender ratios (female/male) were 1.75 for the patient group and 2.55 for the nonclinical sample. T-test revealed a significant difference in age between groups [t(437.7)=8.39, P<.0001], and chi-square test revealed a significant difference in gender distribution (χ2=9.41, P=.002). Cronbach's alpha reliability scores for the entire scale were 0.92 for CFS patients and 0.88 for the
Discussion
This study investigates the psychometric properties of the CFQ.
PCA conducted on the 11-item scale revealed two components, namely, physical and mental fatigue, emerging from the CFS patients and a community sample. This finding is consistent with the initial validation study of the scale in the general population [7] but does not concur with the findings of Morriss et al. [14] in CFS patients. In support of the two-component solution emerging from our data, there is a strong cross-validation of
Acknowledgments
Trudie Chalder acknowledges the financial support from the Department of Health via the National Institute for Health Research (NIHR) Specialist Biomedical Research Centre for Mental Health award to South London and Maudsley NHS Foundation Trust (SLaM) and the Institute of Psychiatry at King's College London.
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