title: The use of differential item functioning analyses to identify cultural differences in responses to the EORTC QLQ-C30.
abstract: BACKGROUND
  The European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30 is a widely used health-related quality of life instrument. The main aim of this study is to investigate whether there are international differences in response to the questionnaire that can be explained by cultural factors.
  
  
  METHODS
  Analyses involved a database of 106 separate studies including data from over 28,000 respondents. Differential item functioning (DIF) analyses using logistic regression were conducted for each item of the EORTC QLQ-C30 with respect to cultural/geographic group. Results were qualitatively compared with previously reported DIF analyses by translation to explore whether the source of the DIF was more likely to be linguistic or cultural in nature.
  
  
  RESULTS
  Although most response patterns were similar, there were a number of international differences in how the questionnaire was answered. The largest variations were found in the results for Eastern Europe and East Asia. Results for the UK, the US and Australia tended to be similar. Many of the European results followed patterns that were more clearly explained when grouped by translation than when grouped by geographical region.
  
  
  CONCLUSIONS
  Our results suggest that, in general, the EORTC QLQ-C30 is suitable for use in a wide variety of countries and settings. Some response variations that have the potential to affect the results of international studies were identified, but it was not always clear whether the source of the variation was primarily linguistic or cultural.
authors.affiliation: Department of Public Health, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen, AB25 2ZD, UK.
authors.forename: N W
authors.initials: NW
authors.lastname: Scott
authors.forename: P M
authors.initials: PM
authors.lastname: Fayers
authors.forename: N K
authors.initials: NK
authors.lastname: Aaronson
authors.forename: A
authors.initials: A
authors.lastname: Bottomley
authors.forename: A
authors.initials: A
authors.lastname: de Graeff
authors.forename: M
authors.initials: M
authors.lastname: Groenvold
authors.forename: M
authors.initials: M
authors.lastname: Koller
authors.forename: M A
authors.initials: MA
authors.lastname: Petersen
authors.forename: M A G
authors.initials: MA
authors.lastname: Sprangers
mesh_terms: D000328:Adult; D000368:Aged; D003071:Cognition; D003431:Cross-Cultural Comparison; D004644:Emotions; D005060:Europe; D005202:Asia, Eastern; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D008877:Middle East; D009369:Neoplasms / Q000628:therapy*; D009656:North America; D010809:Physical Fitness; D011788:Quality of Life; D011795:Surveys and Questionnaires / Q000592:standards*