• Louise J White and Craig A Velozo.
• Department of Physical Therapy, University of Illinois, Chicago, IL 60612, USA. LJWhite@uic.edu
• Arch Phys Med Rehabil. 2002 Jun 1;83(6):822-31.

ObjectivesTo use Rasch measurement to assess and modify the original classification categories of the Oswestry Low Back Pain Disability Questionnaire (Oswestry), to examine the hypothesis that the items from the Oswestry form a unidimensional construct and a hierarchical representation of low back pain (LBP) disability, and to compare ordinal Likert resultant scores to interval Rasch scaled scores with disability categories serving as a framework.DesignRasch analysis model. Existing Oswestry admission data generated by FOTO were analyzed.SettingStatistical analysis of sample database.ParticipantsA sample of 942 patients with LBP referred for physical therapy between 1993 and 1994.InterventionsNot applicable.Main Outcome MeasuresConstruct validity; disability categories (as assessed by Likert and Rasch models); and fit statistics (infit, outfit as mean squares).ResultsAll items from the Oswestry except the pain item fit the Rasch model. Construct validity of the scale using the Rasch model required the structure of the rating scale to be modified from 6 response levels to 4. A hierarchical representation of LBP disability was supported. A comparison of the disability categories based on Likert and Rasch scaling revealed them to be nonequivalent. The new scaling changed the disability categories for 44% of patients.ConclusionRasch analysis produced disability categories in the Oswestry that are linear and, therefore, useful for quantitatively assessing self-reported disability levels.Copyright 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

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