title: Construct validity of the Swedish version of the revised piper fatigue scale in an oncology sample--a Rasch analysis.
abstract: OBJECTIVE
  Fatigue is a common and distressing symptom in cancer patients due to both the disease and its treatments. The concept of fatigue is multidimensional and includes both physical and mental components. The 22-item Revised Piper Fatigue Scale (RPFS) is a multidimensional instrument developed to assess cancer-related fatigue. This study reports on the construct validity of the Swedish version of the RPFS from the perspective of Rasch measurement.
  
  
  METHODS
  The Swedish version of the RPFS was answered by 196 cancer patients fatigued after 4 to 5 weeks of curative radiation therapy. Data from the scale were fitted to the Rasch measurement model. This involved testing a series of assumptions, including the stochastic ordering of items, local response dependency, and unidimensionality. A series of fit statistics were computed, differential item functioning (DIF) was tested, and local response dependency was accommodated through testlets.
  
  
  RESULTS
  The Behavioral, Affective and Sensory domains all satisfied the Rasch model expectations. No DIF was observed, and all domains were found to be unidimensional. The Mood/Cognitive scale failed to fit the model, and substantial multidimensionality was found. Splitting the scale between Mood and Cognitive items resolved fit to the Rasch model, and new domains were unidimensional without DIF.
  
  
  CONCLUSIONS
  The current Rasch analyses add to the evidence of measurement properties of the scale and show that the RPFS has good psychometric properties and works well to measure fatigue. The original four-factor structure, however, was not supported.
authors: Centre for Person-centred Care, Institute of Health and Care Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Department of Clinical Neuroscience and Rehabilitation, Institute of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors: Asa
authors: A
authors: Lundgren-Nilsson
authors: Centre for Person-centred Care, Institute of Health and Care Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. Electronic address: anna.dencker@gu.se.
authors: Anna
authors: A
authors: Dencker
authors: Centre for Person-centred Care, Institute of Health and Care Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors: Sofie
authors: S
authors: Jakobsson
authors: Centre for Person-centred Care, Institute of Health and Care Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors: Charles
authors: C
authors: Taft
authors: Centre for Person-centred Care, Institute of Health and Care Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Faculty of Medicine & Health, Academic Department of Rehabilitation Medicine, University of Leeds, Leeds, UK.
authors: Alan
authors: A
authors: Tennant
mesh_terms: D000368:Aged; D005221:Fatigue / Q000503:physiopathology* / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000503:physiopathology* / Q000523:psychology* / Q000532:radiotherapy; D011594:Psychometrics / Q000379:methods*; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D013548:Sweden
keywords: Rasch analysis; Revised Piper Fatigue Scale; cancer-related fatigue