Normative score and cut-off value of the Neck Disability Index

Neck pain is a common health problem that restricts activities of daily living. The Neck Disability Index (NDI) was developed to assess disability in patients with neck pain. The normative score and the cut-off value are mandatory to assess an individual patient or a certain patient group for clinically important neck pain with disability, by distinguishing it from nonsignificant pain. The objective of the present study was to determine the normative score and the cut-off value of the NDI.

A total of 1,200 participants who registered with an internet research company were interviewed on the website about their episodes of neck pain during the previous 4 weeks, and completed the online NDI questionnaire. If the participants reported neck pain, they were also asked about the disability in activity of daily living it caused, and the presence of associated symptoms in upper limbs. Disability was defined according to the consensus study on the standardization of back pain definitions. The normative score was determined by calculating the mean in the participants, and the cut-off value was determined by the receiver-operating characteristic curve analysis.

The prevalence of neck pain was 37.8 %. Demographic data of the participants also indicated that they were representative of the normal population in Japan. The mean score was 6.98, and the median was 2. The NDI score was higher in middle age, and at its peak in the 50s age group (50-59 years of age). The female mean was significantly higher. The NDI score was higher in those with upper limb symptoms. We have determined the cut-off value of the NDI to detect neck pain associated with disability to be 15.

The normative score and the cut-off value of the NDI were determined. Our cut-off value is potentially useful in evaluating the therapeutic effectiveness of various interventions for neck pain.