title: The comparability of English, French and Dutch scores on the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F): an assessment of differential item functioning in patients with systemic sclerosis.
abstract: OBJECTIVE
  The Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) is commonly used to assess fatigue in rheumatic diseases, and has shown to discriminate better across levels of the fatigue spectrum than other commonly used measures. The aim of this study was to assess the cross-language measurement equivalence of the English, French, and Dutch versions of the FACIT-F in systemic sclerosis (SSc) patients.
  
  
  METHODS
  The FACIT-F was completed by 871 English-speaking Canadian, 238 French-speaking Canadian and 230 Dutch SSc patients. Confirmatory factor analysis was used to assess the factor structure in the three samples. The Multiple-Indicator Multiple-Cause (MIMIC) model was utilized to assess differential item functioning (DIF), comparing English versus French and versus Dutch patient responses separately.
  
  
  RESULTS
  A unidimensional factor model showed good fit in all samples. Comparing French versus English patients, statistically significant, but small-magnitude DIF was found for 3 of 13 items. French patients had 0.04 of a standard deviation (SD) lower latent fatigue scores than English patients and there was an increase of only 0.03 SD after accounting for DIF. For the Dutch versus English comparison, 4 items showed small, but statistically significant, DIF. Dutch patients had 0.20 SD lower latent fatigue scores than English patients. After correcting for DIF, there was a reduction of 0.16 SD in this difference.
  
  
  CONCLUSIONS
  There was statistically significant DIF in several items, but the overall effect on fatigue scores was minimal. English, French and Dutch versions of the FACIT-F can be reasonably treated as having equivalent scoring metrics.
authors.affiliation: Department of Psychiatry, McGill University, Montréal, Québec, Canada; Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, Canada.
authors.forename: Linda
authors.initials: L
authors.lastname: Kwakkenbos
authors.affiliation: Department of Rheumatology, Sint Maartenskliniek Nijmegen, The Netherlands.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Willems
authors.affiliation: Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, Canada; Department of Medicine, McGill University, Montréal, Québec, Canada.
authors.forename: Murray
authors.initials: M
authors.lastname: Baron
authors.affiliation: Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, Canada; Department of Medicine, McGill University, Montréal, Québec, Canada.
authors.forename: Marie
authors.initials: M
authors.lastname: Hudson
authors.affiliation: Department of Medical Social Sciences, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Cella
authors.affiliation: Department of Rheumatology, Sint Maartenskliniek Nijmegen, The Netherlands.
authors.forename: Cornelia H M
authors.initials: CH
authors.lastname: van den Ende
authors.affiliation: Department of Psychiatry, McGill University, Montréal, Québec, Canada; Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, Canada; Department of Medicine, McGill University, Montréal, Québec, Canada; Departments of Epidemiology, Biostatistics, and Occupational Health, McGill University, Montréal, Québec, Canada; Educational and Counselling Psychology, McGill University, Montréal, Québec, Canada; Psychology, McGill University, Montréal, Québec, Canada; School of Nursing, McGill University, Montréal, Québec, Canada.
authors.forename: Brett D
authors.initials: BD
authors.lastname: Thombs
mesh_terms: D000328:Adult; D000368:Aged; D002908:Chronic Disease; D005006:Ethnicity; D005221:Fatigue / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology*; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D012307:Risk Factors; D012595:Scleroderma, Systemic / Q000150:complications* / Q000628:therapy; D044465:White People