Reliability, responsiveness and interpretability of the neck disability index-Dutch version in primary care

To establish an evidence-based recommendation for the pragmatic use of the Neck Disability Index-Dutch Version (NDI-DV) in primary care based on an assessment of the reliability, the responsiveness, and the interpretability of the NDI-DV. At baseline, the NDI-DV was completed by 337 patients with neck pain presenting to 97 chiropractic clinics in Belgium and the Netherlands. Three months after inclusion, 265 patients provided data to assess the responsiveness and interpretability. Reliability was assessed in 155 patients (retested after 10 days) by calculating the intra-class correlation coefficient for agreement (ICCagreement) and the measurement error (standard error of measurement, SEM), the latter resulting in the smallest detectable change (SDC). The minimal important change (MIC) was assessed by the anchor-based MIC distribution using self-reported perceived recovery as anchor. We tested interpretability by relating SDC to MIC. The ICCagreement was 0.88. The SEMagreement was 1.95 resulting in a SDC of 5.40. The NDI-DV appeared to be responsive, being able to distinguish improved from stable patients with an area under the curve of 0.85. The MIC was 4.50. The NDI-DV has good reliability and responsiveness and may be used in clinical practice in Belgium and the Netherlands. A change score of 5 is important for patients, but has a 7 % chance to be due to measurement error.