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Factor analysis of symptoms among subjects with unexplained chronic fatigue: what can we learn about chronic fatigue syndrome?
Nisenbaum R, Reyes M, Unger ER, Reeves WC.Factor analysis of symptoms among subjects with unexplained chronic fatigue: what can we learn about chronic fatigue syndrome?
Journal of Psychosomatic Research 56:171-178, 2004
Summary
Patients with unexplained chronic fatigue also report a variety of other symptoms. The CDC research team was interested in determining whether these symptoms could be categorized into distinct groups. We used a statistical technique called factor analysis to explore data collected from 1,391 fatigued subjects who participated in the Wichita Longitudinal Surveillance Study. This statistical tool identifies the factors associated with an illness and has a system for scoring subjects on each factor according to the symptoms they report. Three symptom groups or factors were elicited: musculoskeletal, infection, and cognition-mood-sleep. The team used another statistical tool, called cluster analysis, to further analyze the factor scores to see if there were distinct groups of persons. Three clusters were identified representing persons with few or no symptoms, a moderate number of symptoms, and a high number of symptoms. Although most CFS subjects were included in the third cluster, there were some that belonged to the second cluster with other persons with less severe, unexplained illness. CFS symptomatology is a multidimensional phenomenon overlapping with other unexplained fatiguing syndromes and this must be considered in CFS research.
Abstract
Objective: Chronic fatigue syndrome (CFS) case definitions agree that fatigue must be unexplained, debilitating and present for at least 6 months, but they differ over accompanying symptoms. Our objective was to compare the 1994 CFS case defining symptoms with those identified by factor analysis.
Methods: We surveyed the Wichita population and measured the occurrence of 21 symptoms in 1391 chronically fatigued subjects who did not report fatigue-associated medical or psychiatric conditions. We used factor analyses to identify symptom dimensions of fatigue and cluster analysis to assign subjects to subgroups.
Results: Forty-three subjects had CFS. We confirmed three factors: musculoskeletal, infection and cognition-mood-sleep, essentially defined by CFS symptoms. Although factor scores were higher among CFS subjects, CFS and non-CFS distributions overlapped substantially. Three clusters also showed overlap between CFS and non-CFS subjects.
Conclusion: CFS symptomatology is a multidimensional phenomenon overlapping with other unexplained fatiguing syndromes and this must be considered in CFS research.
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