Rasch Analysis and Clinical Interpretation of the Modified Oswestry Low Back Pain Disability Questionnaire

Ying-Chih Wang^1*, Jay Kapellusch¹, Bhagwant Sindhu¹, Leigh Lehman², Xiaoyan Li³ & Sheng-Che Yen⁴

¹Department of Occupational Science & Technology, University of Wisconsin Milwaukee, Milwaukee, WI, USA
²Department of Occupational Therapy, Augusta University, Augusta, GA, USA
³Department of Physical Medicine and Rehabilitation, University of Texas Medical School at Houston, and TIRR Memorial Hermann Research Center, Houston, TX, USA
⁴Department of Physical Therapy, Northeastern University, 360 Huntington Ave, Boston, MA, 2115, USA

Ying-Chih Wang, Department of Occupational Science & Technology, University of Wisconsin-Milwaukee, Enderis Hall 955, 2400 E Hartford Ave, Milwaukee, WI 53211.

Keywords: Rasch Analysis; Lumbar Spine; Outpatient Rehabilitation; Low Back Pain; Psychometric Analysis

Abstract

Background
Lumbar spine impairments affect a substantial proportion of individuals.
Objective
Our purposes were to: (1) examine the psychometric properties of the 10-item modified Oswestry Low Back Pain Disability Questionnaire (m-ODI) (0-100) questionnaire using the Rasch analysis, (2) establish the percentile rank of an m-ODI score and (3) develop a functional staging approach to guide clinical interpretation of the patient’s improvement by interpreting m-ODI scores.
Design
Cross-sectional.
Setting
Outpatient rehabilitation clinics.
Patients
28,751 patients with orthopedic lumbar spine impairments seeking outpatient physical therapy in 652 clinics.
InterventionNA
Measurements
We examined rating scale structure, item difficulty hierarchy, item fit, person-item match, separation index, differential item functioning (DIF) by demographic variables, test precision, and unidimensionality of the m-ODI. Additionally, we reported the percentile rank distribution and applied the keyform approach to develop a functional staging.
Results
Results showed that m-ODI questionnaire has adequate psychometric properties. Item ‘lifting’ appeared to be the most difficult item, followed by ‘pain intensity’ and ‘personal care” was the easiest item. The coverage of m-ODI items matched well with the patient functional abilities. With a separation index equaled to 2.10, the m-ODI items can differentiate persons into 3.1 statistically distinct person strata. The m-ODI was free from DIF by gender and symptom acuity, but 3 items exhibited DIF by age group. Factor analysis supported one-factor solution; nonetheless, the first factor explained merely 48.6% of the total variance. We provided an example of functional staging application.
Limitations
Since this study was a secondary analysis of prospectively collected data, selection bias is inevitable.
Conclusions
Results supported the clinical usage of the m-ODI questionnaire in outpatient (orthopedic) rehabilitation service.

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