Validation of the Albanian Neck Disability Index: A Reliable and Precise Tool for Assessing Disability in Young...

Background: Chronic neck pain is a prevalent musculoskeletal condition associated with functional limitations and reduced quality of life, representing a significant public health concern. The Neck Disability Index (NDI) is one of the most widely used patient-reported outcome measures for assessing neck-related disability. Although validated in multiple languages, a comprehensive psychometric evaluation of an Albanian version in a large clinical sample has been lacking. Methods: A methodological cross-sectional study was conducted to translate, culturally adapt, and evaluate the psychometric properties of the Albanian version of the NDI. The translation process followed standardized forward-backward cross-cultural adaptation procedures with authorization from the MAPI Research Trust. A total of 377 individuals with chronic cervical pain completed the questionnaire. Structural validity was assessed using Principal Component Analysis (PCA). Internal consistency was evaluated using Cronbach's alpha, and test-retest reliability was assessed using intraclass correlation coefficients (ICC). Measurement error was estimated using the Standard Error of Measurement (SEM) and Minimal Detectable Change at the 95% confidence level (MDC95) at both item and total score levels. Results: Sampling adequacy was excellent (KMO = 0.948; Bartlett's test p < 0.001). Structural validity supported a predominantly unidimensional structure, with a dominant component explaining 64.17% of the total variance. Internal consistency was excellent (Cronbach's α = 0.99). Test-retest reliability was outstanding, with item-level ICC values ranging from 0.980 to 0.992 and a total score ICC of 0.989. Measurement error for the total score was low (SEM = 0.94; MDC95 = 2.60), indicating that changes greater than 2.60 points reflect real change beyond measurement error. Item-level MDC95 ranged from 0.36 to 0.67. Conclusions: The Albanian version of the NDI demonstrates strong structural validity, excellent internal consistency, high test-retest reliability, and low measurement error in individuals with chronic cervical pain. These findings are most applicable to relatively young, convenience-based Albanian-speaking populations, reflecting the characteristics of the study sample.