title: Are scores on English and French versions of the PHQ-9 comparable? An assessment of differential item functioning.
abstract: BACKGROUND
  Medical research increasingly utilizes patient-reported outcome measures administered and scored in different languages. In order to pool or compare outcomes from different language versions, instruments should be measurement equivalent across linguistic groups. The objective of this study was to examine the cross-language measurement equivalence of the Patient Health Questionnaire-9 (PHQ-9) between English- and French-speaking Canadian patients with systemic sclerosis (SSc).
  
  
  METHODS
  The sample consisted of 739 English- and 221 French-speaking SSc patients. Multiple-Indicator Multiple-Cause (MIMIC) modeling was used to identify items displaying possible differential item functioning (DIF).
  
  
  RESULTS
  A one-factor model for the PHQ-9 fit the data well in both English- and French-speaking samples. Statistically significant DIF was found for 3 of 9 items on the PHQ-9. However, the overall estimate in depression latent scores between English- and French-speaking respondents was not influenced substantively by DIF.
  
  
  CONCLUSIONS
  Although there were several PHQ-9 items with evidence of minor DIF, there was no evidence that these differences influenced overall scores meaningfully. The PHQ-9 can reasonably be used without adjustment in Canadian English- and French-speaking samples. Analyses assessing measurement equivalence should be routinely conducted prior to pooling data from English and French versions of patient-reported outcome measures.
authors.affiliation: Department of Psychiatry, McGill University, Montréal, Québec, Canada.
authors.forename: Erin
authors.initials: E
authors.lastname: Arthurs
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Steele
authors.forename: Marie
authors.initials: M
authors.lastname: Hudson
authors.forename: Murray
authors.initials: M
authors.lastname: Baron
authors.forename: Brett D
authors.initials: BD
authors.lastname: Thombs
mesh_terms: D002170:Canada; D005260:Female; D006306:Health Surveys / Q000592:standards*; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods / Q000592:standards*; D012595:Scleroderma, Systemic / Q000175:diagnosis*; D057566:Self Report; D011795:Surveys and Questionnaires / Q000592:standards*