Psychometric Validation and Population-Based Normative Values of the Japanese Oswestry Disability Index Version 2.1a: A Nationally Representative Survey.

BACKGROUND CONTEXT: The Oswestry Disability Index (ODI) is one of the most widely used instruments for assessing disability related to low back pain (LBP). However, population-based normative values are scarce, and the structural validity of Japanese version of the ODI (version 2.1a) has not been sufficiently evaluated. PURPOSE: To psychometrically validate the Japanese version of the ODI (version 2.1a) and to establish population-based normative values stratified by age and LBP duration. STUDY DESIGN/SETTING: Population-based cross-sectional study using a nationwide survey in Japan. PATIENT SAMPLE: A nationally representative sample of community-dwelling adults in Japan selected through a two-stage stratified random sampling design. A total of 5,000 individuals were invited to participate. OUTCOME MEASURES: Self-report measures: Disability related to low back pain assessed using the Japanese version of the ODI (version 2.1a). METHODS: Japan was stratified into 65 strata, from which 250 sampling points were randomly selected, and 20 residents were randomly sampled per point. Psychometric properties of the ODI version 2.1a were evaluated among respondents using factor analyses. Response-adjusted, survey-weighted normative values were estimated for the general population and for individuals with LBP, stratified by age group and pain duration subtype (acute, subacute, and chronic). RESULTS: Of the 5,000 individuals invited, 2,188 responded (response rate 43.8%). Among respondents, 1,270 had complete ODI data and were included in the psychometric analysis, including 173 individuals with LBP. The estimated population prevalence of LBP was 14.7% (95% confidence interval CI 13.1-16.4%), comprising acute 2.5% (95% CI 1.9-3.3%), subacute 1.1% (95% CI 0.7-1.7%), and chronic 11.1% (95% CI 9.8-12.5%). Factor analyses demonstrated a unidimensional structure of the ODI version 2.1a. Among individuals with LBP, the survey-weighted mean ODI score was 20.23 (95% CI 18.32-22.13). Normative values varied by pain duration (acute: 12.54 95% CI 8.87-16.22; subacute: 13.54 95% CI 8.78-18.31; chronic: 22.74 95% CI 20.56-24.92) and increased with advancing age. CONCLUSION: This study provides psychometric validation of the Japanese ODI version 2.1a and establishes age- and pain duration-specific normative values. These findings support the use of ODI version 2.1a as a single total score for profiling disability in everyday life and for evaluating the management of LBP in both clinical practice and research.