title: Confirmatory factor analysis and item response theory analysis of the Whiteley Index. Results from a large population based study in Norway. The Hordaland Health Study (HUSK).
abstract: OBJECTIVE
  The Whiteley Index (WI) is a widely used screening instrument for health anxiety/hypochondriasis. Several studies have previously explored the psychometric properties of the WI, but with mixed findings concerning both item composition and factor structure. The main aim of the current study was to examine different factor structures as identified from previous studies using data from a large general population based study. We also wanted to provide gender specific norms.
  
  
  METHODS
  Data were taken from a large population-based study in Norway, the Hordaland Health Study (HUSK N=7274). Confirmatory factor analysis (CFA) of several models of the WI was conducted. Item response theory (IRT) analysis was performed on the model with the best goodness-of-fit.
  
  
  RESULTS
  CFA of all previously proposed factor models of the WI revealed clearly inadequate model fits. The IRT analysis suggested that a six-item model best described the data, and CFA confirmed an adequate goodness-of-fit across indices.
  
  
  CONCLUSIONS
  The current study found evidence for a six-item, single-factor model of the WI. Our findings suggest that this abbreviated version has the best factor structure compared to previously proposed factor models. We recommend that the factor structure identified in this study should be investigated further in independent samples.
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway; Division of Mental Health, Norwegian Institute of Public Health, Bergen, Norway; Department of Medicine, Haraldsplass Deaconess Hospital, Bergen, Norway. Electronic address: karielisev@gmail.com.
authors.forename: Kari-Elise Frøystad
authors.initials: KE
authors.lastname: Veddegjærde
authors.affiliation: Division of Mental Health, Norwegian Institute of Public Health, Bergen, Norway; Uni Health, Uni Research, Bergen, Norway; Department of Psychiatry, Helse Fonna HF, Haugesund, Norway.
authors.forename: Børge
authors.initials: B
authors.lastname: Sivertsen
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway; Department of Medicine, Haraldsplass Deaconess Hospital, Bergen, Norway.
authors.forename: Ingvard
authors.initials: I
authors.lastname: Wilhelmsen
authors.affiliation: Division of Mental Health, Norwegian Institute of Public Health, Bergen, Norway; Uni Health, Uni Research, Bergen, Norway; Alcohol and Drug Research Western Norway, Stavanger University, Hospital Stavanger, Stavanger, Norway.
authors.forename: Jens Christoffer
authors.initials: JC
authors.lastname: Skogen
mesh_terms: D000328:Adult; D000368:Aged; D001007:Anxiety / Q000175:diagnosis / Q000453:epidemiology*; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D006998:Hypochondriasis / Q000175:diagnosis / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D011594:Psychometrics
keywords: Factor structure; Health anxiety; Hypochondriasis; Item response theory analysis; Population based study; Whiteley Index