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

ABSTRACT: 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) in order to allow its use with Italian-speaking patients with neck pain (NP).summary of bockground data. growing attention is being given to standardised outcome measures to improve interventions for neck pain. A translated form of the NDI has never been validated in Italian patients with NP.Methods. The NDI-I was developed by means of forward-backward translation, a final review by an expert committee, and a test of the pre-final version to establish its correspondence with the original english version. The psychometric testing included factor analysis, reliability by internal consistency (Cronbach's alpha) and test-retest reliability (intraclass coefficient correlation, ICC), construct validity by comparing NDI-I with the neck pain and disability scale (NPDS), a numerical rating scale (NRS), the Hospital Anxiety and Depression Score (HADS), and the Short-Form Health Survey (SF-36) (spearman's correlation), and sensitivity to change by calculating the smallest detectable change (SDC).results. The questionnaire was administered to 101 subjects with chronic NP and proved to be acceptable. Factor analysis revealed a two-factor 10-item solution (explained variance: 56%). The questionnaire showed good internal consistency (α = 0.842) and test-retest reliability (ICC = 0.846). Construct validity showed a good correlation with NPDS (rho = 0.687), moderate correlations with the NRS (rho = 0.545), and HADS (rho = 0.422 for the Anxiety score and rho = 0.546 for the Depression score), and poor correlations with the SF-36 subscales (rho = 0.066 to -0.286). The psychometric analyses of the subscales and total scale were similar. The SDC 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.