Psychometric evaluation of the Oswestry Disability Index in patients with chronic low back pain: factor and Mokken analyses.

BACKGROUND: Disputes exist regarding the psychometric properties of the Oswestry Disability Index (ODI). The present study was to examine the reliability, validity, and dimensionality of a Chinese version of the ODI version 2.1 in a sample of 225 adult orthopedic outpatients with chronic low back pain [mean age (SD): 40.7 (11.4) years]. METHODS: We conducted reliability analysis, exploratory bifactor analysis, confirmatory factor analysis, and Mokken scale analysis of the ODI. To validate the ODI, we used the Short-Form 36 questionnaire (SF-36) and visual analog scale (VAS). RESULTS: The reliability, and discriminant and construct validities of the ODI was good. The fit statistics of the unidimensional model of the ODI were inadequate. The ODI was a weak Mokken scale (Hs = 0.31). CONCLUSIONS: The ODI was a reliable and valid scale suitable for measurement of disability in patients with low back pain. But the ODI seemed to be multidimensional that was against the use of the raw score of the ODI as a measurement of disability.