Reliability, validity, and responsiveness of the Japanese version of the Neck Pain and Disability Scale

Until recently, no Japanese versions have existed of the more popular, patient-reported disability questionnaires for neck pain. This study aimed to test the reliability, validity, and responsiveness of the Japanese version of the Neck Pain and Disability Scale (NPDS), one of the most widely used questionnaires in patients with neck pain. In this validation study, 167 outpatients with neck pain participated. Patients received the NPDS and the Medical Outcome Study Short Form 36-item Health Survey (SF-36), and used Visual Analog Scales (VASs) to assess pain and global health. To examine test-retest reliability, patients who were considered stable by clinicians were given the NPDS 2 weeks after baseline. To examine responsiveness, patients who had not undergone treatment at the time of the first data collection or had no change in treatment over 3 months were studied again 2 weeks after starting a new medication or physical therapy. Of the 167 participants, 143 completed the questionnaires (85.6%). Factor analysis showed two factors, defined as neck-pain-related disability (factor 1) and neck-related pain (factor 2). Cronbach's alpha coefficient for factor 1, factor 2, and total score was 0.94, 0.93, and 0.96. The intra-class correlation coefficients for the 19 more stable patients were 0.79, 0.88, and 0.87. For concurrent validity, the correlation between NPDS subscales and total score and SF-36 subscale scores ranged from r = -0.54 to -0.22 (p < 0.01). Correlations between the NPDS subscales and total score and VAS of pain ranged from 0.56 to 0.77 (p < 0.01) and those for VAS of global health ranged from 0.48 to 0.63 (p < 0.01). The NPDS subscales and total scores of the 41 patients retested after treatment were significantly improved. The Japanese version of the NPDS is a useful scale with reliability, validity, and responsiveness in assessing patients suffering from neck pain.