title: Differential item functioning impact in a modified version of the Roland-Morris Disability Questionnaire.
abstract: OBJECTIVE
  To evaluate a modified version of the Roland-Morris Disability Questionnaire for differential item functioning (DIF) related to several covariates.
  
  
  BACKGROUND
  DIF occurs in an item when, after controlling for the underlying trait measured by the test, the probability of endorsing the item varies across groups.
  
  
  METHODS
  Secondary data analysis of two studies of participants with back pain (total n = 875). We used a hybrid item response theory/ logistic regression approach for detecting DIF. We obtained scores that accounted for DIF. We evaluated the impact of DIF on individual and group scores, and compared scores that ignored or accounted for DIF in terms of the strength of association with SF-36 subscale scores.
  
  
  RESULTS
  DIF was found in 18/23 items. Salient scale-level differential functioning was found related to age, education, and employment. Overall 24 participants (3%) had salient scale-level differential functioning. Mean scores across demographic groups differed minimally when accounting for DIF. The strength of association of scores with SF-36 scores was similar for scores that ignored and scores that accounted for DIF.
  
  
  CONCLUSIONS
  The modified version of the Roland-Morris Disability Questionnaire appears to have largely negligible DIF related to the covariates assessed here.
authors: Department of Medicine, University of Washington, Harborview Medical Center, 325 Ninth Avenue, Box 359780, Seattle, WA 98104, USA. pcrane@u.washington.edu
authors: Paul K
authors: PK
authors: Crane
authors: Karynsa
authors: K
authors: Cetin
authors: Karon F
authors: KF
authors: Cook
authors: Kurt
authors: K
authors: Johnson
authors: Richard
authors: R
authors: Deyo
authors: Dagmar
authors: D
authors: Amtmann
mesh_terms: D000203:Activities of Daily Living; D000293:Adolescent; D000328:Adult; D001416:Back Pain / Q000175:diagnosis* / Q000503:physiopathology; D004185:Disability Evaluation; D016002:Discriminant Analysis; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011446:Prospective Studies; D011594:Psychometrics / Q000295:instrumentation*; D011788:Quality of Life; D016032:Randomized Controlled Trials as Topic; D018434:Sickness Impact Profile; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires / Q000592:standards*