Reliability and responsiveness of the Norwegian version of the Neck Disability Index
Johansen, J. B.; Roe, C.; Bakke, E.; Mengshoel, A. M.; Andelic, N.
Scandinavian Journal of Pain
Background and aim: The Norwegian version of the Neck Disability Index (NDI) has been widely used in previous studies. To our knowledge, the test-retest reliability and responsiveness of the NDI have not been investigated. Thus, the aim of the present study was to investigate the test-retest reliability and responsiveness of the Norwegian version of the NDI in neck pain patients seen in a specialized outpatient clinic. Methods: This study included patients referred to the neck and back outpatient clinic at Oslo University Hospital. A total of 255 patients were included in the study, of which 42 participated in the test-retest portion of the study. The intraclass correlation coefficient (ICC) was used to assess test-retest reliability. A total of 113 patients participated in the responsiveness analyses. Based on their responses on the Global Rating Scale of Change (GRS), patients were categorized into the following groups: worsened (n=24), unchanged (n=7) and improved (n=62). The minimal detectable change (MDC) for the NDI was calculated. Responsiveness was assessed by constructing a Receiver Operating Characteristic curve (ROC curve) to distinguish patients who had improved or worsened from those who remained unchanged. The minimum clinically important difference (MCID) was estimated. Results: The test-retest reliability between the baseline scores and the retest NDI scores was very good (ICC=0.84; 95% CI 0.72-0.91). The ability of the NDI to discriminate between improved and unchanged patients (responsiveness) over time was acceptable based on the ROC curve analysis (AUC=0.70; 95% CI 0.58-0.82). The estimated MDC for the Norwegian version of the NDI is 12.3%, and the MCID is 16.6%. Conclusion: The Norwegian version of the NDI proved to be an instrument with good test-retest reliability and acceptable responsiveness for assessing neck pain-related disability among neck pain patients in a specialized outpatient clinic. 2013 Scandinavian Association for the Study of Pain.