title: Are chronic fatigue and chronic fatigue syndrome valid clinical entities across countries and health-care settings?
abstract: OBJECTIVE
  The validity of the diagnosis of chronic fatigue syndrome and related chronic fatigue states remains controversial, particularly in psychiatry. This project utilized international epidemiological and clinical research data to test construct validity across diagnostic categories, health-care settings and countries. Relevant demographic, symptom and diagnostic data were obtained from 33 studies in 21 countries. The subjects had fatigue lasting 1-6 months (prolonged fatigue), or >6 months (chronic fatigue), or met diagnostic criteria for chronic fatigue syndrome.
  
  
  METHODS
  Common symptom domains were derived by factor analytic techniques. Mean scores on each symptom factor were compared across diagnostic categories, health-care settings and countries.
  
  
  RESULTS
  Data were obtained on 37,724 subjects (n = 20,845 female, 57%), including from population-based studies (n = 15,749, 42%), studies in primary care (n = 19 472, 52%), and secondary or specialist tertiary referral clinics (n = 2503, 7%). The sample included 2013 subjects with chronic fatigue, and 1958 with chronic fatigue syndrome. A five-factor model of the key symptom domains was preferred ('musculoskeletal pain/fatigue', 'neurocognitive difficulties', 'inflammation', 'sleep disturbance/fatigue' and 'mood disturbance') and was comparable across subject groups and settings. Although the core symptom profiles were similar, some differences in symptoms were observed across diagnostic categories, health-care settings and between countries.
  
  
  CONCLUSIONS
  The construct validity of chronic fatigue and chronic fatigue syndrome is supported by an empirically derived factor structure from existing international datasets.
authors.affiliation: Brain and Mind Research Institute, Camperdown, NSW, Australia. ianh@med.usyd.edu.au
authors.forename: Ian
authors.initials: I
authors.lastname: Hickie
authors.forename: Tracey
authors.initials: T
authors.lastname: Davenport
authors.forename: Suzanne D
authors.initials: SD
authors.lastname: Vernon
authors.forename: Rosane
authors.initials: R
authors.lastname: Nisenbaum
authors.forename: William C
authors.initials: WC
authors.lastname: Reeves
authors.forename: Dusan
authors.initials: D
authors.lastname: Hadzi-Pavlovic
authors.forename: Andrew
authors.initials: A
authors.lastname: Lloyd
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003431:Cross-Cultural Comparison; D003430:Cross-Sectional Studies; D003625:Data Collection / Q000706:statistics & numerical data; D015673:Fatigue Syndrome, Chronic / Q000175:diagnosis* / Q000453:epidemiology / Q000523:psychology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009460:Neurologic Examination; D009483:Neuropsychological Tests; D055815:Young Adult