title: Construct validity and test-retest reliability of the Fatigue Severity Scale in people with chronic neck pain.
abstract: OBJECTIVE
  To investigate an appropriate scoring system and unidimensionality using Rasch analysis, discriminant validity, and reliability of the Fatigue Severity Scale (FSS) in people with chronic neck pain.
  
  
  METHODS
  Cross-sectional.
  
  
  METHODS
  Tertiary institution.
  
  
  METHODS
  Patients with chronic neck pain (n=100) and asymptomatic controls (n=40).
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  The FSS.
  
  
  RESULTS
  Twenty-six of the 100 participants with chronic neck pain agreed to complete the FSS again within 1 week after the first administration for the assessment of the test-retest reliability. Two items obviously threatening unidimensionality were eliminated, and the 7-item FSS was developed through Rasch analyses. The 7-item FSS demonstrated the appropriateness of its 7-point scale and adequate internal consistency (Rasch-generated reliability, .83-.91). The 7-item FSS had a negligible floor effect (1%) and ceiling effect (2%). The item-person map demonstrated limited distribution of item difficulty in comparison with the distribution of person ability. The chronic neck pain group demonstrated significantly (P<.001) higher scores in the 7-item FSS than the control group, indicating discriminant validity. The 7-item FSS also demonstrated adequate test-retest reliability with a mean interval of 4.1 days (n=26) for each item (quadratic-weighted κ=.83-.94), and as a whole (intraclass correlation coefficient=.95). A 0-to-100 scale table reflecting Rasch scores was developed, and the minimum detectable change was 9.5 in the 0 to 100 scale.
  
  
  CONCLUSIONS
  The 7-item FSS appears unidimensional and reliable, and can be used quickly in clinical practice to gain a basic understanding of fatigue symptoms in people with chronic neck pain. Further, it is possible to modify the 7-item FSS to enhance discriminant ability within people with chronic neck pain by adding additional items, enlarging the distribution of item difficulty.
authors.affiliation: NHMRC Centre of Clinical Research Excellence-Spinal Pain, Injury and Health, Division of Physiotherapy, School of Health and Rehabilitation Science, The University of Queensland, Brisbane, QLD 4072, Australia. h.takasaki@uq.edu.au
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takasaki
authors.forename: Julia
authors.initials: J
authors.lastname: Treleaven
mesh_terms: D000328:Adult; D002908:Chronic Disease; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005221:Fatigue / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000453:epidemiology*; D026741:Physical Therapy Modalities; D015203:Reproducibility of Results; D062606:Tertiary Care Centers; D013997:Time Factors