Responsiveness of the Neck Disability Index in patients with mechanical neck disorders
From: Spine J. 2009 Jul 24. [Epub ahead of print]
The purpose of this study was to report the test-retest reliability, construct validity, minimum clinically important difference, and minimal detectable change for the Neck Disability Index.
Cohort study of patients presenting to outpatient physical therapy clinics. Ninety-one subjects with a primary complaint of neck pain, with or without concomitant upper extremity symptoms, who were participants in a randomized clinical trial. Neck Disability Index and the 15-point Global Rating of Change self-report measures. All subjects completed the Neck Disability Index at baseline and at a 3-week follow-up. Additionally, subjects completed the Global Rating of Change scale, which was used to dichotomize patients into improved or stable groups. Changes in the Neck Disability Index were used to assess test-retest reliability, construct validity, minimum clinically important difference, and minimal detectable change.
Test-retest reliability was moderate for the Neck Disability Index (intraclass correlation coefficient, 0.64; 95% confidence interval, 0.19-0.84). For the Neck Disability Index, the minimum clinically important difference was 7.5 points and the minimal detectable change was 10.2 points. The Neck Disability Index appears to demonstrate adequate responsiveness based on statistical reference criteria when used in a sample that approximates the high percentage of patients with neck pain and concomitant upper extremity referred symptoms. Because the minimum clinically important difference is within the bounds of measurement error, a 10-point change (the minimal detectable change) should be used as the minimum clinically important difference.
