Development of the Italian Version of the Neck Disability Index Cross-cultural Adaptation, Factor Analysis, Reliability, Validity, and Sensitivity to Change

Study Design. Evaluation of the psychometric properties of a translated and culturally adapted questionnaire. Objective. Translating, culturally adapting, and validating the Italian version of the Neck Disability Index (NDI-I) to allow its use with Italian-speaking patients with neck pain (NP). Summary of Background Data. More attention is being given to standardized outcome measures to improve interventions for NP. A translated form of the NDI has never been validated in Italian patients with NP. Methods. The NDI-I was developed by forward-backward translation, a final review by an expert committee, and a test of the prefinal version to establish its correspondence with the original English version. The psychometric testing included factor analysis, reliability by internal consistency (Cronbach alpha) and test-retest reliability (intraclass coefficient correlation), construct validity by comparing NDI-I with the Neck Pain and Disability Scale, a numerical rating scale, the Hospital Anxiety and Depression Scale, and the 36-Item Short Form Health Survey (Spearman correlation), and sensitivity to change by calculating the smallest detectable change. Results. The questionnaire was administered to 101 subjects with chronic NP and proved to be acceptable. Factor analysis revealed a 2-factor 10-item solution (explained variance: 56%). The questionnaire showed good internal consistency (alpha = 0.842) and test-retest reliability (intraclass coefficient correlation = 0.846). Construct validity showed a good correlation with Neck Pain and Disability Scale (rho = 0.687), moderate correlations with the numerical rating scale (rho = 0.545), and Hospital Anxiety and Depression Scale (rho = 0.422 for the Anxiety score and rho = 0.546 for the Depression score), and poor correlations with the 36-Item Short Form Health Survey subscales (rho = 0.066 to -0.286). The psychometric analyses of the subscales and total scale were similar. The smallest detectable change of the NDI-I was 3. Conclusion. The NDI was successfully translated into Italian and proved to have a good factorial structure and psychometric properties that replicated the results of other versions. Its use is recommended for research purposes.