• Feng Xie, Hua Ye, Yu Zhang, Xia Liu, Ting Lei, and Shu-Chuen Li.
• Department of Clinical Epidemiology and Biostatistics, McMaster University, ON, Canada. fengxie@mcmaster.ca
• Int J Rheum Dis. 2011 May 1;14(2):206-10.

ObjectiveTo validate the Oxford Knee Score (OKS) in outpatients with knee osteoarthritis (OA).MethodsEligible 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.ResultsThe 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).Conclusion  The OKS has demonstrated good psychometric properties and thus can be considered a reliable and valid measurement for outpatients with OA.© 2010 The Authors. International Journal of Rheumatic Diseases © 2010 Asia Pacific League of Associations for Rheumatology and Blackwell Publishing Asia Pty Ltd.

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