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) 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 α) 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 (α = 0.842) and test-retest reliability (intraclass coefficient correlation = 0.846). Construct validity showed a good correlation with Neck Pain and Disability Scale (ρ = 0.687), moderate correlations with the numerical rating scale (ρ = 0.545), and Hospital Anxiety and Depression Scale (ρ = 0.422 for the Anxiety score and ρ = 0.546 for the Depression score), and poor correlations with the 36-Item Short Form Health Survey subscales (ρ = 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.