title: Item-level informant discrepancies across obese-overweight children and their parents on the PedsQL™ 4.0 instrument: an iterative hybrid ordinal logistic regression.
abstract: OBJECTIVE
  Child obesity has become a major health concern worldwide. In order to provide successful intervention strategies, it is necessary to understand how obese-overweight children and their parents perceive obesity and its consequences on child's health-related quality of life (HRQoL). This study aimed to assess measurement equivalence of the PedsQL™ 4.0 across obese-overweight children and their parents.
  
  
  METHODS
  The items in the PedsQL™ 4.0 were analysed for differential item functioning (DIF) across obese-overweight children and their parents using an iterative hybrid ordinal logistic regression/item response theory approach. The sample included 647 overweight-obese children and their parents, who completed child and parent reports of the PedsQL™ 4.0, respectively.
  
  
  RESULTS
  Overall, 17 out of 23 (74%) items were flagged with DIF across two groups: eight items exhibited uniform DIF and nine items non-uniform DIF. In addition, parents of obese children rated the child's HRQoL significantly lower than their children in all domains of the PedsQL™ 4.0, and this finding did not change whether or not items with uniform DIF were included.
  
  
  CONCLUSIONS
  Although obese-overweight children and their parents interpret items of the PedsQL™ 4.0 in a conceptually different manner, removing or retaining DIF items in the subscales had no significant effects on group differences. Accordingly, it appears that observed differences in HRQoL scores across child and parent reports are a true difference and not a reflection of measurement artefact.
authors.affiliation: Department of Biostatistics, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Peyman
authors.initials: P
authors.lastname: Jafari
authors.affiliation: Department of Biostatistics, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Elahe
authors.initials: E
authors.lastname: Allahyari
authors.affiliation: Department of Biostatistics, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Mina
authors.initials: M
authors.lastname: Salarzadeh
authors.affiliation: Department of Biostatistics, Shiraz University of Medical Sciences, Shiraz, Iran. zbagheri@sums.ac.ir.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Bagheri
mesh_terms: D001294:Attitude to Health; D002648:Child; D005260:Female; D006304:Health Status; D006801:Humans; D007492:Iran; D016015:Logistic Models; D008297:Male; D010290:Parents / Q000523:psychology*; D063766:Pediatric Obesity / Q000523:psychology*; D011788:Quality of Life / Q000523:psychology*; D011795:Surveys and Questionnaires
keywords: Children; Differential item functioning; Obese; Parents; Quality of life