title: Extension from inpatients to outpatients: validity and reliability of the Oxford Knee Score in measuring health outcomes in patients with knee osteoarthritis.
abstract: OBJECTIVE
  To validate the Oxford Knee Score (OKS) in outpatients with knee osteoarthritis (OA).
  
  
  METHODS
  Eligible patients were interviewed using a pretested questionnaire containing the OKS, the Short Form (SF)-6D, and the EuroQol Group 5-Dimension Self-Report Questionnaire score (EQ-5D). Reliability was assessed using Cronbach's alpha, dimensionality using principal component factor analysis and item-total correlations, convergent and discriminant construct validity using expected correlations between the OKS and the SF-6D and the EQ-5D.
  
  
  RESULTS
  The OKS were well accepted by patients in a pilot testing. When administered to a convenient sample of 187 patients with knee OA (mean age 64 years, 74% female, mean duration of OA 7.6 years), Cronbach's alpha exceeded 0.8 and factor analysis yielded two factors with eigenvalues > 1. Hypothesized item-total correlations (ρ ≥ 0.4) were observed for all items. Convergent construct validity was supported by the presence of hypothesized moderate to strong correlations between the OKS and SF-6D physical functioning, role limitation, social functioning and pain, EQ-5D mobility, self-care, usual activities, and pain/discomfort, and mobility visual analogue scale (ρ = 0.47-0.82). Discriminant construct validity was not satisfactory. The OKS correlated weakly with SF-6D vitality (ρ = 0.35), but strongly with SF-6D mental health and EQ-5D anxiety/depression (ρ = 0.51 and 0.41, respectively).
  
  
  CONCLUSIONS
  The OKS has demonstrated good psychometric properties and thus can be considered a reliable and valid measurement for outpatients with OA.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, ON, Canada. fengxie@mcmaster.ca
authors.forename: Feng
authors.initials: F
authors.lastname: Xie
authors.forename: Hua
authors.initials: H
authors.lastname: Ye
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.forename: Xia
authors.initials: X
authors.lastname: Liu
authors.forename: Ting
authors.initials: T
authors.lastname: Lei
authors.forename: Shu-Chuen
authors.initials: SC
authors.lastname: Li
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D002681:China; D004185:Disability Evaluation; D016002:Discriminant Analysis; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D007297:Inpatients; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis* / Q000503:physiopathology / Q000523:psychology / Q000628:therapy; D010045:Outpatients; D010146:Pain / Q000175:diagnosis / Q000503:physiopathology; D010147:Pain Measurement; D011237:Predictive Value of Tests; D025341:Principal Component Analysis; D011379:Prognosis; D011594:Psychometrics; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires