Minimal clinically important change of the neck disability index and the numerical rating scale for patients with neck pain

Study Design. Prospective, single-cohort study. Objective. To assess the minimal clinically important change (MCIC) on the Neck Disability Index (NDI) and the Numerical Rating Scale (NRS) for pain in patients with neck pain. Summary of Background Data. Both measurement instruments are frequently used in research and clinical practice, but which changes are clinically relevant is still unknown. Methods. The MCIC was estimated with 2 different methods, both integrating an anchor-based and distribution-based approach: the minimal detectable change (MDC) and the optimal cutoff point of the ROC curve. The study population consisted of 183 patients with nonspecific neck pain. Results. The results show an MDC of 10.5 points for the NDI (scale range, 0-50) and 4.3 points for the NRS (scale range, 0-10), and optimal cutoff points of the ROC curve of 3.5 for the NDI and 2.5 for the NRS. Conclusion. The estimated MCIC should be used as an indication for relevant changes in clinical practice. Using the optimal cutoff point of the ROC curve, false positives and false negatives are equally weighted; and if there are no objections doing so, the optimal cutoff point of the ROC curve may be a good choice.