Cross-cultural Adaptation, Reliability, Validity, and Responsiveness of the Simplified-Chinese Version of Neck Disability Index

Study Design. Cross-cultural adaptation and psychometric evaluation. Objective. The aim of this study was to translate the Neck Disability Index (NDI) into the simplified-Chinese language and to evaluate the reliability, validity, and responsiveness of the new questionnaire. Summary of Background Data. Neck pain is a major health problem resulting in major disability. NDI is the most frequently used scale for self-rating of disability due to neck pain. At present, there is no simplified-Chinese version of the NDI. The aims of this study were to culturally adapt and translate the NDI into the simplified-Chinese language (NDI-SC) and to evaluate its psychometric properties in patients with neck pain. Methods. The NDI was translated into simplified-Chinese version based on established guidelines. A total of 70 patients participated in this study. Patients were asked to complete a set of questionnaires comprising of their demographic information, the NDI-SC, and a visual analog scale (VAS) of pain. Fifty-six patients returned after 1 to 2 weeks to complete the same set of questionnaires and the global rating of change (GROC) scale. Then, the NDI-SC was evaluated for content validity, construct validity, internal consistency, test-retest reliability, and responsiveness. Results. The NDI-SC demonstrated excellent internal consistency (Cronbach α = 0.92) and good test-retest reliability (ICC 2,1 = 0.85). Content validity was confirmed as no floor or ceiling effects were detected for the NDI-SC total score. Construct validity was established with factor analysis revealing two-factor subscales explaining 66% of the variance. The NDI-SC showed a strong correlation with VAS (Rp = 0.61, P < 0.001) and a moderate correlation with GROC (Rs = 0.46, P < 0.001). The correlation between NDI-SC change scores and VAS change scores was also moderate (R p = 0.59, P < 0.001). Conclusion. The results showed that the NDI-SC is a reliable, valid, and responsive instrument to measure functional limitations in patients with neck pain. Level of Evidence: 3