Abstract
BackgroundThe 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.MethodsA 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.ResultsThe 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.ConclusionsOur 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.
Highlights
The Oswestry Disability Index (ODI) is widely used for patients with back pain
The 10 items of ODI contributed a unidimensional construct measuring the different levels of functional limitation; the difficulties of these items were well targeted to the person ability without skewing toward the lower or higher levels of disability
The ODI version 2.1 is a unidimensional questionnaire with high reliability, and well estimates the disability level of back pain without skewing toward the lower or higher levels of disability
Summary
The Oswestry Disability Index (ODI) is widely used for patients with back pain. few studies have examined its psychometric properties using modern measurement theory. The Oswestry Disability Index (ODI) is one of the most widely used disease-specific self-administered questionnaires for measuring back pain [2,3]. Strict examination of the psychometric properties of the ODI by modern measurement theory is needed for precise measurement of the level of functional limitation in back pain. Total scores are used in CTT to represent the latent traits of subjects without concern for differences in difficulty of individual items. The Rasch model uses the probability of a subject’s response to individual items as the latent traits. The Rasch model transforms ordinal scores into interval scores along the logit scale [7,8], which successfully ranks the item difficulty among items, thereby overcoming the scoring problems of CTT. The changes in the logit scale will be a more precise and valid indicator of changes in a client's ability than are the changes in an ordinal scale
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