title: Measurement precision of the disability for back pain scale-by applying Rasch analysis.
abstract: BACKGROUND
  The Oswestry Disability Index (ODI) is widely used for patients with back pain. However, few studies have examined its psychometric properties using modern measurement theory. The purpose of this study was to investigate the psychometric properties of the ODI in patients with back pain using Rasch analysis.
  
  
  METHODS
  A total of 408 patients with back pain participated in this cross-sectional study. Patients were recruited from the orthopedic, neurosurgery, rehabilitation departments and pain clinic of two hospitals. Rasch analysis was used to examine the Chinese version of ODI 2.1 for unidimensionality, item difficulty, category function, differential item functioning, and test information.
  
  
  RESULTS
  The fit statistics showed 10 items of the ODI fitted the model's expectation as a unidimensional scale. The ODI measured the different levels of functional limitation without skewing toward the lower or higher levels of disability. No significant ceiling and floor effects and gaps among the items were found. The reliability was high and the test information curve demonstrated precise dysfunction estimation.
  
  
  CONCLUSIONS
  Our results showed that the ODI is a unidimensional questionnaire with high reliability. The ODI can precisely estimate the level of dysfunction, and the item difficulty of the ODI matches the person ability. For clinical application, using logits scores could precisely represent the disability level, and using the item difficulty could help clinicians design progressive programs for patients with back pain.
authors.affiliation: Department of Orthopaedics, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Yen-Mou
authors.initials: YM
authors.lastname: Lu
authors.forename: Yuh-Yih
authors.initials: YY
authors.lastname: Wu
authors.forename: Ching-Lin
authors.initials: CL
authors.lastname: Hsieh
authors.forename: Chih-Lung
authors.initials: CL
authors.lastname: Lin
authors.forename: Shiuh-Lin
authors.initials: SL
authors.lastname: Hwang
authors.forename: Kuang-I
authors.initials: KI
authors.lastname: Cheng
authors.forename: Yi-Jing
authors.initials: YJ
authors.lastname: Lue
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001416:Back Pain / Q000150:complications; D059350:Chronic Pain; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results