Development, validity and reliability of the Italian version of the Copenhagen neck functional disability scale.

Background: Valid and reliable patient-reported outcome measures support health professionals in evaluating the results of clinical research and practice. The Copenhagen Neck Functional Disability Scale (CNFDS) has shown promising measurement properties to measure disability in patients with neck pain, but an Italian version of this questionnaire is not available. The objective of this study was to cross-culturally adapt the CNFDS into Italian (CNFDS-I), and to assess its validity and reliability in patients with neck pain. Methods: The CNFDS-I was developed according to well-established guidelines for cross-cultural adaptation of patient-reported outcome measures. A cross-sectional clinimetric study was conducted to evaluate its validity and reliability. Patients with chronic neck pain (pain > 3 months) participated in this study. The following measurement properties (defined by the COSMIN initiative) were assessed: structural validity (exploratory factor analysis), internal consistency (Cronbach’s α), construct validity [by testing hypotheses on expected correlations with the Neck Disability Index (NDI), the Neck Bournemouth Questionnaire (NBQ), and pain Visual Analogue Scale (VAS)]. Testretest reliability [Intraclass Correlation Coefficient for agreement (ICCagreement)], and measurement error [Smallest Detectable Change (SDC)] were also assessed in 50 clinically stable patients. Floor/ceiling effects and acceptability were calculated. Results: One-hundred and sixty-two patients (mean age = 47.9 ± 14.5 years, 70% female) were included. The CNFDS-I exhibited sufficient unidimensionality (one factor explained 83% of the variability) and internal consistency (α = 0.83). Construct validity was sufficient as all correlations with the other questionnaires were as expected (r = 0. 846 with NDI, r = 0.708 with NBQ, r = 0.570 with VAS). Test-retest reliability was excellent (ICCagreement = 0.99, 95% CI from 0.995 to 0.999), while measurement error was equal to 8.31 scale points (27% scale range). No floor/ceiling effects were detected. The average time for filling the questionnaire was two minutes. Conclusions: The CNFDS-I proved to be a valid and reliable outcome measure to assess disability in patients with chronic neck pain. Head-to-head comparison studies on the CNFDS-I measurement properties against other disability measures for neck pain (e.g. NDI and NBQ) are required to determine the relative merits of these different measures.