THE RELIABILITY AND VALIDITY OF THE VERNON AND MOIR NECK DISABILITY INDEX AND COMPARISON TO THE SHORT FORM-36 HEALTH SURVEY QUESTIONNAIRE

Abstract

Introduction: The NDI is a simple 10-item questionnaire used to assess patients with neck pain. The original validation was performed on 52 patients with neck pain and the test-retest on 17 whiplash patients with a 2-day interval. The SF36 measures functional ability, wellbeing and the overall health of patients. It is used in health economics to assess the health utility, gain and economic impact of medical interventions.

Objectives: (1) Independently validate the NDI in patients with neck pain. (2) Draw comparison of the NDI and SF36.

Subjects: 100 patients with neck pain attending the spinal clinic completed self-assessment questionnaires. A second questionnaire was completed in 30 patients after a period of 1–2 weeks.

Statistics: The internal consistency of the NDI and SF36 was calculated using Cronbach alpha. The test-retest reliability and the concurrent validity between the two questionnaire scores were assessed using Pearson correlation. Individual scores for each of the ten items of the NDI were correlated to the total disability score categories.

Results: Both questionnaires showed robust internal consistency – alpha for NDI = 0.85 (95% CI = 0.8–0.89) and SF36 = 0.84 (95% CI = 0.79–0.88). The NDI had significant correlation to all eight domains of the SF36 (p< 0.001). The individual scores for each of the ten items had significant correlation with the total disability score (p< 0.001). The test-retest reliability of the NDI was acceptable.

Conclusions: We have shown irrefutably that the NDI has good reliability and validity and that it stands up well to the SF36.