Measurement precision of the disability for back pain scale-by applying Rasch analysis
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RESEARCH
Open Access
Measurement precision of the disability for back pain scale-by applying Rasch analysis Yen-Mou Lu1,2, Yuh-Yih Wu3, Ching-Lin Hsieh4,5, Chih-Lung Lin6,7, Shiuh-Lin Hwang6,7, Kuang-I Cheng8 and Yi-Jing Lue9,10,11*
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. Keywords: Back pain, Rasch analysis, Oswestry disability index, Functional measure, Disability
Background Back pain is a common health problem and one of the most costly conditions in many countries [1]. Thus, it is essential to use a precise tool to assess pain and disability. The Oswestry Disability Index (ODI) is one of the most widely used disease-specific self-administered questionnaires for measuring back pain [2,3]. The questionnaire assesses the pain problem and the resulting functional disability [4]. 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.
* Correspondence: [email protected] 9 Department of Physical Therapy, College of Health Science, Kaohsiung Medical University, Kaohsiung, Taiwan 10 Neurology and Master’s Program in Neurology, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan Full list of author information is available at the end of the article
Compared with traditional classical test theory (CTT), the Rasch model overcomes the drawbacks of scoring. In CTT, the person’s ability and the difficulty of each item cannot be estimated separately; the score of each ite
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