Study design: Cross-sectional study.
Objective: To analyze the psychometric properties of the neck disability index (NDI), with a special emphasis in its factor structure, and its usefulness, in a sample of patients suffering from a subacute whiplash problem.
Summary of background data: A valid and reliable instrument to assess pain-related disability would be of great help to clinicians and researchers interested in whiplash associated disorders. First, to better understand the impact of whiplash on the patient's life, and his or her progress over time. Second, to formulate comprehensive treatment plans, and evaluate the results from therapeutic actions. Finally, to follow-up patients' changes and improvement. The NDI could be an appropriate instrument for these purposes.
Methods: A convenience sample of 150 subacute whiplash patients participated. They were requested to complete the Catalan version of the NDI, and report about their pain intensity, pain interference and depression. RESULTS.: An exploratory factor analysis showed that the NDI can be viewed as a 2-factor instrument. The items and the instrument's total score were normally distributed. Internal consistency was also appropriate both for the total score (Cronbach's alpha: 0.87) and the 2 subscales (0.7 for the pain and interference with cognitive functioning scale, and 0.83 for the physical functioning scale). Total NDI and subscales scores significantly correlated with pain intensity, pain interference, and depression.
Conclusion: The NDI showed excellent psychometric properties in a sample of subacute whiplash patients. Additional research is needed to replicate the NDIs factor structure.