The Neck Disability Index (NDI) was developed in 1989 by
Howard Vernon. The Index was developed as a modification of the
Oswestry Low Back Pain Disability Index with the permission of
the original author (J. Fairbank, 1980). In 1991, Vernon and Mior
published the results of a study of reliability and validity in
the Journal of Manipulative and Physiologic Therapeutics. Since
then, approximately ten articles have appeared in the indexed
literature on the NDI. All of these studies have confirmed the
original reports of a high level of reliability and validity. We
currently know that the NDI consists of one factor - "physical
disability" - although NDI scores correlate well with SF-36
mental component scores as well. We know that the minimum
detectable score and the minimal clinically important difference
amounts to the same figure - 5 NDI points.
The NDI has become a standard instrument for measuring
self-rated disability due to neck pain and is used by clinicians
and researchers alike.
Each of the 10 items is scored from 0 - 5. The maximum score
is therefore 50. The obtained score can be multiplied by 2 to
produce a percentage score. Occasionally, a respondent will not
complete one question or another. The average of all other items
is then added to the completed items.
The original report provided scoring intervals for
interpretation, as follows:
0 - 4 = no disability
5 - 14 = mild
15 - 24 = moderate
25 - 34 = severe
above 34 = complete.
Please note: This means 15-24 out of 50 (the RAW SCORE)
equates with moderate disability.
It is recommended that the NDI be used at baseline and for
every 2 weeks thereafter within the treatment program to measure
progress. As noted above, at least a 5-point change is required
to be clinically meaningful. Patients often do not score the
items as zero, once they are in treatment. In other words, it is
common to find that patients will continue to score between 5 -
15 despite having made excellent recovery (i.e., they may be back
to work). The practitioner should avoid the trap of "treating
till zero", as this is not supportable based on current evidence.