title: Do people with and without medical conditions respond similarly to the short health anxiety inventory? An assessment of differential item functioning using item response theory.
abstract: OBJECTIVE
  Individuals with medical conditions are likely to have elevated health anxiety; however, research has not demonstrated how medical status impacts response patterns on health anxiety measures. Measurement bias can undermine the validity of a questionnaire by overestimating or underestimating scores in groups of individuals. We investigated whether the Short Health Anxiety Inventory (SHAI), a widely-used measure of health anxiety, exhibits medical condition-based bias on item and subscale levels, and whether the SHAI subscales adequately assess the health anxiety continuum.
  
  
  METHODS
  Data were from 963 individuals with diabetes, breast cancer, or multiple sclerosis, and 372 healthy individuals. Mantel-Haenszel tests and item characteristic curves were used to classify the severity of item-level differential item functioning in all three medical groups compared to the healthy group. Test characteristic curves were used to assess scale-level differential item functioning and whether the SHAI subscales adequately assess the health anxiety continuum.
  
  
  RESULTS
  Nine out of 14 items exhibited differential item functioning. Two items exhibited differential item functioning in all medical groups compared to the healthy group. In both Thought Intrusion and Fear of Illness subscales, differential item functioning was associated with mildly deflated scores in medical groups with very high levels of the latent traits. Fear of Illness items poorly discriminated between individuals with low and very low levels of the latent trait.
  
  
  CONCLUSIONS
  While individuals with medical conditions may respond differentially to some items, clinicians and researchers can confidently use the SHAI with a variety of medical populations without concern of significant bias.
authors.affiliation: University of Regina, Canada.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: LeBouthillier
authors.affiliation: University of Regina, Canada.
authors.forename: Michel A
authors.initials: MA
authors.lastname: Thibodeau
authors.affiliation: University of Regina, Canada.
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Alberts
authors.affiliation: University of Regina, Canada.
authors.forename: Heather D
authors.initials: HD
authors.lastname: Hadjistavropoulos
authors.affiliation: University of Regina, Canada. Electronic address: Gordon.Asmundson@uregina.ca.
authors.forename: Gordon J G
authors.initials: GJ
authors.lastname: Asmundson
mesh_terms: D000328:Adult; D001007:Anxiety / Q000209:etiology*; D001943:Breast Neoplasms / Q000523:psychology; D002908:Chronic Disease / Q000523:psychology*; D003920:Diabetes Mellitus / Q000523:psychology; D005239:Fear; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000523:psychology; D015588:Observer Variation; D011594:Psychometrics; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*
keywords: Differential item functioning; Item characteristic curves; Item response theory; Medical conditions; Short Health Anxiety Inventory; Test characteristic curves