The Reliability and Validity of Neck Disability Index-Urdu Mobile App in Chronic Mechanical Neck Pain Patients

Abstract

Background: Neck pain is prevalent and disabling, and literacy barriers may limit accurate completion of written patient-reported outcome measures in Urdu-speaking populations. A voice-supported mobile application version of the Urdu Neck Disability Index (NDI-U App) may improve accessibility but requires psychometric evaluation. Objective: To determine the reliability, internal consistency, structural validity, and convergent construct validity of the NDI-U App in adults with chronic mechanical neck pain. Methods: A cross-sectional observational psychometric validation study was conducted across three centers in Kotli, Azad Kashmir, Pakistan (2023). Adults aged 18–65 years with chronic mechanical neck pain (≥3 months) completed the NDI-U App, Urdu Northwick Park Neck Pain Questionnaire (NPQ-U), and Visual Analogue Scales (VAS) for pain and disability at baseline; the NDI-U App was repeated after 48 hours. Test–retest reliability was assessed using ICC(2,1); internal consistency using Cronbach’s alpha; floor/ceiling effects using extreme-score proportions; convergent validity using Pearson correlations; and structural validity using principal component analysis with varimax rotation. Results: Among 300 participants, test–retest reliability was excellent (ICC=0.95; 95% CI: 0.93–0.96; p<0.001) with SEM=1.73 and MDC95=4.79. Internal consistency was fair (α=0.675; 95% CI: 0.63–0.72). Floor and ceiling effects were minimal (1.0% and 0.3%, respectively). Convergent validity was moderate with NPQ-U (r=0.584; 95% CI: 0.50–0.66; p<0.001) and weak with VAS pain (r=0.253) and disability (r=0.266) (both p<0.001). Two components explained 33.34% variance (KMO=0.584; Bartlett p<0.001). Conclusion: The NDI-U App demonstrates excellent reliability, minimal extreme-score effects, and moderate convergent validity, supporting its clinical and research use for disability assessment in Urdu-speaking chronic mechanical neck pain populations.