title: Factors determining fatigue in the chronic fatigue syndrome: a path analysis.
abstract: OBJECTIVE
  To explore the interrelationship of different dimensions (fatigue, neuroticism, sleep quality, global mental and physical health) in patients with chronic fatigue syndrome (CFS).
  
  
  METHODS
  Patients meeting the Fukuda criteria of CFS filled out two independent fatigue scales (Fatigue Questionnaire, FQ and Checklist Individual Strength, CIS), NEO-Five Factor Inventory (NEO-FFI), Pittsburgh Sleep Quality Index (PSQI) and Medical Outcomes Study 36-item Short Form Health Survey (SF36). Exploratory and confirmatory path analyses were performed.
  
  
  RESULTS
  Out of 226 eligible patients, 167 subjects were included (mean age 39.13 years, SD 10.14, 92% female). In a first exploratory path analysis, using FQ for assessment of fatigue, night-time PSQI sleep quality had a direct effect on SF36 physical quality of life (PQoL) and no effect on FQ fatigue. This was confirmed by a subsequent path analysis with CIS fatigue and by confirmatory path analyses in 81 patients. These unexpected results raised the question whether FQ or CIS fatigue sufficiently operationalizes fatigue in CFS patients.
  
  
  CONCLUSIONS
  Poor sleep quality seems to directly impact on mental quality of life (MQoL) and PQoL without mediation of fatigue assessed with FQ and CIS. A more cohesive framework needs to be developed with more comprehensive clinical tools for the different dimensions in the construct of CFS.
authors.affiliation: a Department of General Internal Medicine , University Hospital Ghent , Ghent , Belgium.|b Department of General Internal Medicine, Centre for Neurophysiologic Monitoring , University Hospital Ghent , Ghent , Belgium.
authors.forename: Els
authors.initials: E
authors.lastname: Tobback
authors.affiliation: a Department of General Internal Medicine , University Hospital Ghent , Ghent , Belgium.
authors.forename: Ignace
authors.initials: I
authors.lastname: Hanoulle
authors.affiliation: a Department of General Internal Medicine , University Hospital Ghent , Ghent , Belgium.|b Department of General Internal Medicine, Centre for Neurophysiologic Monitoring , University Hospital Ghent , Ghent , Belgium.
authors.forename: An
authors.initials: A
authors.lastname: Mariman
authors.affiliation: a Department of General Internal Medicine , University Hospital Ghent , Ghent , Belgium.|b Department of General Internal Medicine, Centre for Neurophysiologic Monitoring , University Hospital Ghent , Ghent , Belgium.
authors.forename: Liesbeth
authors.initials: L
authors.lastname: Delesie
authors.affiliation: c Sleep Medicine Centre, Kempenhaeghe Foundation , Heeze , The Netherlands.|d Faculty of Medicine and Health Sciences, Department of Internal Medicine , University of Ghent , Ghent , Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: Pevernagie
authors.affiliation: a Department of General Internal Medicine , University Hospital Ghent , Ghent , Belgium.|b Department of General Internal Medicine, Centre for Neurophysiologic Monitoring , University Hospital Ghent , Ghent , Belgium.|d Faculty of Medicine and Health Sciences, Department of Internal Medicine , University of Ghent , Ghent , Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: Vogelaers
keywords: CIS; Chronic fatigue syndrome; FQ; PSQI; SF36