title: Differential item functioning related to ethnicity in an oral health-related quality of life measure.
abstract: OBJECTIVE
  To assess whether an oral health-related quality of life (OHRQoL)measure showed differential item functioning (DIF) by ethnicity.
  
  
  METHODS
  A simple random sample of 12- and 13-year-old schoolchildren enrolled in the Taranaki District Health Board's school dental service, New Zealand. Each child (n = 430) completed the Child Perception Questionnaire (CPQ(11-14)) in the dental clinic waiting room, prior to a dental examination. The dataset included age, gender, ethnicity, and deprivation status. The general principle of the analytic plan was that equal scores from each CPQ(11-14) item were expected from both non-Mäori and Mäori groups regardless of their ethnic group. Ordinal logistic regression was performed. The dependent variables were the CPQ(11-14) items. The ethnicity group and each CPQ(11-14) domain score were the independent variables. Non-uniform DIF was assessed through adding an interaction term for each CPQ(11-14) sub-scale.
  
  
  RESULTS
  Non-uniform DIF was found in two items, one in the Functional Limitations sub-scale and another in the Social Well-being sub-scale. Uniform DIF was found in one item of the Emotional Well-being sub-scale.
  
  
  CONCLUSIONS
  Both non-uniform and uniform DIF by ethnicity was found in three of 37 items of the CPQ(11-14) questionnaire, showing it is important to perform DIF analysis when applying OHRQoL measures.
authors.affiliation: Public Dental Health Research Group, Universidade do Sul de Santa Catarina, Tubarão, Brazil. jefferson.traebert@unisul.br
authors.forename: Jefferson
authors.initials: J
authors.lastname: Traebert
authors.forename: Lyndie A
authors.initials: LA
authors.lastname: Foster Page
authors.forename: W Murray
authors.initials: WM
authors.lastname: Thomson
authors.forename: David
authors.initials: D
authors.lastname: Locker
mesh_terms: D000293:Adolescent; D002648:Child; D003431:Cross-Cultural Comparison; D003753:Dental Health Surveys; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D009520:New Zealand; D009909:Oral Health; D011788:Quality of Life