Study design: Translation and psychometric testing.
Objective: To adapt the neck disability index (NDI) cross-culturally to Arabic language and to investigate the reliability and validity of the Arabic version of NDI in an Arabic-speaking sample with neck pain.
Summary of background data: Although largely used, no previous reports exist on the translation process or the testing of the psychometric properties of the Arabic version of the NDI.
Methods: Cross-cultural adaptation of an outcome questionnaire. The English version of the NDI was translated into Arabic (NDI-Ar) and back-translated according to established guidelines. Sixty-five patients with neck pain completed the NDI -Ar twice during a 1-week period, to assess its test-retest reliability. Further psychometric testing was done by assessing internal consistency, construct validity (factor structure), and responsiveness.
Results: The internal consistency value (Cronbach α) for the NDI-Ar was 0.89. The test-retest reliability (intraclass correlation coefficient) was excellent at 0.96 (95% confidence interval from 0.93 to 0.97). There was a significant correlation (r = 0.92, P < 0.05) between the scores obtained from the first administration of the NDI-Ar and the second administration. Factor analysis demonstrated a 2-factor structure, explaining 67.58% of total variance. The analysis of responsiveness was calculated with an unpaired t test after 1 week of treatment and demonstrating a statically significant difference between stable and improved patients (P < 0.05). The Spearman correlation coefficient (rS = 0.81; P = 0.000) revealed strong relation between the change in score in the NDI-Ar and global rating of change. No ceiling or floor effects were detected in the NDI-Ar.
Conclusion: The Arabic version of the NDI has a 2-factor 10-item structure and is a reliable, valid, and responsive tool that can be used to assess neck pain in Arabic-speaking patients with neck pain. Therefore, it can be recommended for clinical and research purposes.