Journal of Manipulative and Physiological Therapeutics
State-of-the-Art PapersThe Neck Disability Index: State-of-the-Art, 1991-2008
Section snippets
History of the Neck Disability Index
Before 1991, no instrument was available to assess the self-rated disability of patients with neck pain. In the previous decade, a few of such instruments for patients with low back pain had been developed, chiefly, the Oswestry Low Back Pain Index (OI)1 and the Roland-Morris Low Back Pain Questionnaire.2 Recognizing the deficiency with respect to neck pain, Vernon undertook to develop a similar instrument suitable for patients with neck pain. It was decided to model this instrument on the OI,
Scoring and Interpretation
Each item is scored out of 5 for a maximum total score of 50. Care should be taken in reporting the score as either out of 50 or as a percentage out of 100. Most studies have reported the scores out of 50. Several strategies for dealing with missing data or noncompliance with an item have been developed. When only 1 item is missing, some authors have scored the NDI out of 45 and converted the score to a percentage. When several items are missing, some authors have used the mean value of the
The Original 1991 Report
The original study reported on test-retest reliability over a 2-day period, obtaining a value of 0.89 (P < .05). Internal consistency was measured using Cronbach α, with a total index value of .80. The highest scoring items (average out of 5) were the following: headaches = 2.6; lifting = 2.2; recreation = 2.2; reading = 2.1; and driving = 2.0. The total index scores of the study sample were normally distributed, as follows: 0 to 4 (none) = 2%; 5 to 14 (mild) = 35%; 15 to 24 (moderate) = 48%;
Methods
The search strategy for the current report for articles using or referring to the NDI was conducted as a citation search of the 1991 publication using Science Citation Index, through the Scholar's Portal Web of Science. Articles were retrieved from 1991 to December 2007. Articles were reviewed to insure that the instrument used in assessing the self-rating of disability by patients with neck pain was actually the NDI. This resulted in 287 qualified citations. These articles were then classified
Psychometric Properties
Since 1991, 22 additional publications have reported on the psychometric properties of the NDI.5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 Eight of these were published before 20025, 6, 7, 8, 9, 10, 11, 12 and most of these were included in the only systematic review to date.27 In that review, it was acknowledged that (1) the NDI was the most widely used of the several scales for self-rating disability in patients with neck pain, which had been developed
Conclusion
The current “state-of-the-art” of the NDI has been reviewed here. The NDI is the oldest and most widely used instrument for self-reporting of disability due to neck pain. Its internal psychometric properties have been well established in numerous cultural groups with neck pain: it is highly reliable, strongly internally consistent, and with a 1-factor structure for “physical disability.” It has strong and well-documented convergent and divergent validity with other instruments used in the
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