Psychometric validation of the simplified Chinese Copenhagen Neck Functional Disability Scale in patients with chronic nonspecific neck pain

Introduction Reliable and valid measurement tools are crucial for clinical practice in chronic nonspecific neck pain (CNSNP). The Copenhagen Neck Functional Disability Scale (CNFDS) is a widely used scale in neck pain assessment and has its unique advantages, but it is not available for patients with CNSNP in southern China. Objective To develop the simplified Chinese version of CNFDS (CNFDS-SC) cross-culturally and to investigate its measurement properties in patients with CNSNP. Design Cross-sectional study. Setting Validation of neck pain measurement scale in southern China. Patients One hundred five patients with CNSNP. Interventions Not applicable. Main Outcome Measures Internal consistency and test-retest reliability were evaluated using Cronbach's alpha and intraclass correlation coefficient (ICC), respectively. Construct validity and structural validity were validated by hypothesis testing and exploratory factor analysis, respectively. Internal and external responsiveness were validated. Interpretability was revealed by the standard error of measurement (SEM) and smallest detectable change (SDC). Results Internal consistency (Cronbach's alpha = 0.77 for first test and 0.84 for retest) and test-retest reliability (ICC = 0.95) were satisfactory. CNFDS-SC scores showed strong correlations with the numeric rating scale (NRS), the Neck Disability Index (NDI), and the Northwick Park Neck Pain Questionnaire (NPQ) scores (r = 0.652, 0.763, and 0.719, respectively; p < .001). Factor analysis revealed a one-factor structure of the scale. Regarding responsiveness, the standardized response mean (SRM) and the Guyatt's responsiveness index (GRI) were 1.29 and 2.12, respectively. CNFDS-SC change scores showed good correlations with the anchoring question (r = 0.619, p < .001), NDI (r = 0.439, p = .001), and NPQ (r = 0.438 p = .001) change scores; the area under the receiver-operating characteristic (ROC) curve was 0.89 (p < .001). The SEM and SDC were 0.93 and 2.57, respectively. No floor or ceiling effect and no missing items were observed. Conclusion The CNFDS-SC was demonstrated with adequate reliability, validity, responsiveness, and interpretability. The CNFDS-SC could be an effective tool for the clinical assessment of patients with CNSNP in southern China.