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Crosscultural Adaptation, Reliability, and Validity of the Japanese Version of the Neck Disability Index

Study Design. Translation and psychometric testing. Objective. To translate and culturally adapt the Neck Disability Index (NDI) and to assess the reliability and validity of the Japanese version of the NDI (NDI-J) in Japanese outpatients with neck pain. Summary of Background Data. To date, no previous report exists on the translation process and psychometric testing of the NDI-J. Methods. The NDI was translated and culturally adapted into Japanese in accordance with published guidelines. A total of 110 outpatients with neck pain participated in the study. Psychometric testing included reliability by internal consistency (Cronbach &agr;) and test-retest reliability (intraclass correlation coefficient), factor analysis, convergent validity by comparing the NDI-J with the short-form health survey (Pearson correlation) and responsiveness (unpaired t tests, standard error of measurement, and minimal detectable change). Results. The Cronbach &agr; of the NDI-J was 0.88 and the intraclass correlation coefficient for test-retest reliability was 0.91 (95% confidence interval, 0.82–0.95). Factor analysis demonstrated a 2-factor structure, explaining 61.8% of the total variance. The correlation between the NDI-J and the short-form health survey, version 36, subscales ranged from good to fair (−0.25 to −0.51). The analysis of responsiveness was calculated with an unpaired t test after 3 weeks of treatment demonstrating a statistically significant difference between the stable and improved patients (P ⩽ 0.05). The standard error of measurement and minimal detectable change were calculated as 2.9 and 6.8, respectively. Conclusion. The NDI-J is a valid, reliable, and responsive tool that can be used to assess neck pain in Japanese outpatients.