title: Factor analysis of symptoms among subjects with unexplained chronic fatigue: what can we learn about chronic fatigue syndrome?
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.
  
  
  CONCLUSIONS
  CFS symptomatology is a multidimensional phenomenon overlapping with other unexplained fatiguing syndromes and this must be considered in CFS research.
authors.affiliation: Viral Exhanthems and Herpesvirus Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases/CDC, 1600 Clifton Road, Mail Stop A-15, Building 6, Room 116, Atlanta, GA 30333, USA. ran7@cdc.gov
authors.forename: Rosane
authors.initials: R
authors.lastname: Nisenbaum
authors.forename: Michele
authors.initials: M
authors.lastname: Reyes
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Unger
authors.forename: William C
authors.initials: WC
authors.lastname: Reeves
mesh_terms: D016000:Cluster Analysis; D005163:Factor Analysis, Statistical; D015673:Fatigue Syndrome, Chronic / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires