ORIGINAL PAPER
Psychometric validation of the Spanish neck disability index and development of a shortened 5-item version for chronic neck pain
1
Exercise and Rehabilitation Sciences Institute, School of Physical Therapy, Faculty of Rehabilitation Sciences, Universidad Andres Bello, Santiago, Chile
Submission date: 2025-12-08
Acceptance date: 2026-02-24
Online publication date: 2026-10-20
Corresponding author
Hernán Andrés de la Barra Ortiz
Exercise and Rehabilitation Sciences Institute, School of Physical Therapy, Faculty of Rehabilitation Sciences, Universidad Andres Bello, Avenida Fernández Concha 700, Las Condes, Santiago, Chile, Postal code: 7591538
Exercise and Rehabilitation Sciences Institute, School of Physical Therapy, Faculty of Rehabilitation Sciences, Universidad Andres Bello, Avenida Fernández Concha 700, Las Condes, Santiago, Chile, Postal code: 7591538
KEYWORDS
TOPICS
ABSTRACT
Introduction:
Chronic neck pain (CNP) is a prevalent condition that compromises quality of life and functional performance. The neck disability index (NDI) is widely used to assess neck-related disability, yet updated psychometric evidence for Spanish-speaking populations with CNP is limited. This study aimed to validate the Spanish NDI and evaluate the psychometric performance of a shortened clinical form in adults with CNP.
Methods:
A cross-sectional study was conducted in adults with CNP referred to physical therapy (n = 123). Participants completed the Spanish NDI. Construct validity was assessed through exploratory factor analysis (EFA) using Spearman correlations and principal components extraction assuming a one-factor solution, with a 0.40 loading criterion. Sampling adequacy was verified with the Kaiser–Meyer–Olkin index. Internal consistency was examined with Cronbach’s alpha. Confirmatory factor analysis (CFA), using a robust maximum likelihood estimator, evaluated the model fit of the best-performing item set. Model fit indices included the Comparative Fit Index (CFI), Tucker–Lewis Index (TLI), Root Mean Square Error of Approximation (RMSEA), and Standardized Root Mean Square Residual (SRMR).
Results:
A one-factor structure emerged in the EFA, with items S1 (pain), S2 (personal care), S3 (lifting), S4 (reading), and S10 (recreation) showing the strongest loadings. Removing low-loading items improved internal consistency (α = 0.71 vs. 0.64 for the full scale). The CFA supported the reduced 5-item model, demonstrating satisfactory fit (CFI = 0.99, TLI = 0.97, RMSEA = 0.04, SRMR = 0.04), supporting the structural validity of the instrument for assessing disability in individuals with CNP.
Conclusions:
The Spanish NDI demonstrated adequate construct validity in adults with CNP. The shortened 5-item version showed improved internal consistency and strong model fit, offering a clinically efficient alternative for rapid disability screening. Further validation in different populations and clinical contexts is recommended.
Chronic neck pain (CNP) is a prevalent condition that compromises quality of life and functional performance. The neck disability index (NDI) is widely used to assess neck-related disability, yet updated psychometric evidence for Spanish-speaking populations with CNP is limited. This study aimed to validate the Spanish NDI and evaluate the psychometric performance of a shortened clinical form in adults with CNP.
Methods:
A cross-sectional study was conducted in adults with CNP referred to physical therapy (n = 123). Participants completed the Spanish NDI. Construct validity was assessed through exploratory factor analysis (EFA) using Spearman correlations and principal components extraction assuming a one-factor solution, with a 0.40 loading criterion. Sampling adequacy was verified with the Kaiser–Meyer–Olkin index. Internal consistency was examined with Cronbach’s alpha. Confirmatory factor analysis (CFA), using a robust maximum likelihood estimator, evaluated the model fit of the best-performing item set. Model fit indices included the Comparative Fit Index (CFI), Tucker–Lewis Index (TLI), Root Mean Square Error of Approximation (RMSEA), and Standardized Root Mean Square Residual (SRMR).
Results:
A one-factor structure emerged in the EFA, with items S1 (pain), S2 (personal care), S3 (lifting), S4 (reading), and S10 (recreation) showing the strongest loadings. Removing low-loading items improved internal consistency (α = 0.71 vs. 0.64 for the full scale). The CFA supported the reduced 5-item model, demonstrating satisfactory fit (CFI = 0.99, TLI = 0.97, RMSEA = 0.04, SRMR = 0.04), supporting the structural validity of the instrument for assessing disability in individuals with CNP.
Conclusions:
The Spanish NDI demonstrated adequate construct validity in adults with CNP. The shortened 5-item version showed improved internal consistency and strong model fit, offering a clinically efficient alternative for rapid disability screening. Further validation in different populations and clinical contexts is recommended.
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