title: Validating a measure of myalgic encephalomyelitis/chronic fatigue syndrome symptomatology.
abstract: OBJECTIVE
  The present study sought to validate a comprehensive self-report measure of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) symptomatology to aid in clinical and research assessment.
  
  
  METHODS
  Exploratory factor analysis (EFA) was used to establish the underlying factor structure of the DePaul Symptom Questionnaire (DSQ) (Jason, Evans, et al., 2010) using a well-characterized sample of individuals (92.6% met the Fukuda et al. criteria (1994) and/or the Clinical Canadian Criteria (Carruthers et al., 2003)), and this structure was then tested on a less stringently recruited sample of individuals utilizing a confirmatory factor analysis (CFA). Convergent and discriminant validity of the DSQ were also examined utilizing alternative measures of symptomatology and functioning.
  
  
  RESULTS
  A 3-factor solution was found using EFA (Neuroendocrine, Autonomic & Immune Dysfunction; Neurological/Cognitive Dysfunction; Post-Exertional Malaise) and the fit of this factor structure was adequate for the second sample.
  
  
  CONCLUSIONS
  The DSQ is a valid measure of ME/CFS symptomatology. The emergent factors were consistent with previous literature on symptom clusters, and convergent and discriminant validity were established.
authors.affiliation: Center for Community Research/DePaul University/990 W. Fullerton Ave. Suite 3100/Chicago, Illinois 60614/USA.
authors.forename: Abigail A
authors.initials: AA
authors.lastname: Brown
authors.affiliation: Center for Community Research/DePaul University/990 W. Fullerton Ave. Suite 3100/Chicago, Illinois 60614/USA.
authors.forename: Leonard A
authors.initials: LA
authors.lastname: Jason
keywords: DePaul Symptom Questionnaire; case definition; chronic fatigue syndrome; diagnostic criteria; myalgic encephalomyelitis