Neck Disability Index
The NDI is a modification of the Oswestry Low Back Pain Disability Index . It is a patient-completed, condition-specific functional status questionnaire with 10 items including pain, personal care, lifting, reading, headaches, concentration, work, driving, sleeping and recreation. The NDI has sufficient support and usefulness to retain its current status as the most commonly used self-report measure for neck pain .
The NDI is translated in many languages (greek, german, dutch, Korean, Spanish, french) each has its own validity and reliability outcomes. Because there is an impact of translation on validity.
The NDI can be used to evaluate the patients status presence and to evaluate the evolution during the therapy
Intended Population 
- Chronic neck pain
- musculoskeletal neck pain
- whiplash injuries and whiplash associated disorders
- cervical radiculopathy
Method of Use
The NDI can be scored as a raw score or doubled and expressed as a percent . Each section is scored on a 0 to 5 rating scale, in which zero means 'No pain' and 5 means 'Worst imaginable pain'. Al the points can be summed to a total score. The test can be interpretated as a raw score, with a maximum score of 50, or as a percentage.
0 points or 0% means : no activity limitations ,
50 points or 100% means complete activity limitation.
A higher score indicates more patient-rated disability. There is no statement in the original literature on how to handle missing data. To use the NDI for patient decisions, a clinically important change was calculated as 5 points, with a sensitivity of 0.78 and a specificity of 0.80.
Mean duration of the test: 3 to 7.8 minutes 
Some benchmarks can be found in literature but methodologically they were not described and theire validity and reliability are questionable Vernon and Moir presented the following interpretation:
• 0-4points (0-8%) no disability,
• 5-14points ( 10 – 28%) mild disability,
• 15-24points (30-48% ) moderate disability,
• 25-34points (50- 64%) severe disability,
• 35-50points (70-100%) complete disability
Definition : test-retest reliability. When an instrument is tested on two different occasions the reslads should be comparable and preferably identical. The intraclass correlation coefficients between the two results is than calculated.
• Intra-examiner reliability: when two or more tests were preformed by the same executor. With this reliability, the stability of the variables can be determined. Because the NDI is a patient controlled questionnaire, there is no operator involved and the intra-examiner reliability is not relevant.
• Inter-examiner reliability: when two different executors test the same variable. This consist the objectiveness of the tests. Because there is no operator involved the intra-examiner reliability is not relevant.
• Internal consistency : measures if the different parts of the test correlate with each other. The NDI has a reasonable internal consistency³
The NDI has a fair to moderate test-retest reliability in patients with mechanical neck pain but also for patients with cervical radiculopathy . ,. although intra class correlations can change between 0,50 and 0,98 . These difference may occur because some studies do not separate chronic or acute neck pain or due to the fact that the study only used patients with acute neck pain and the retestinterval was 72 hours .
Validity: Does the instrument measure what it is suppose to measure.
Content validity: Are all the different aspects of the measured attribute covered?
Construct validity: validity of subjective construct like pain.
Validity is tested in different trails by comparing NDI with different instruments:
- The PET
- the Visual Analogue scale.
- The Northwick Park Neck Pain Questionnaire: NPNQ
- The Patient-specific Functional Scale: PSFS: [[|]]
- The Disability Rating Index : DRI
They all had strong correlation coefficients suggesting their content is highly comparable: The NDI has a good construct validity.
The NDI is seen as a valide tool to measure neck pain and disabilities in patients with neck pain due to acute or chronic conditions as well as in patients suffering from musculoskeletal dysfunctions, whiplash - associated disorders and cervical radiculopathy. 
The NDI appears to demonstrate adequate responsiveness in patients with neck pain and concomitant upper extremity referred symptoms. Young et al suggest that a 10-point change should be used as the minimum clinically important difference.
MCID-MCIC: the minimal clinically important difference or change (MCID / MCIC) is described as the smallest difference or change that patients perceive as beneficial.. In patients with musculoskeletal related complaints MCID can be said to occur when the changes are over 5 points of change (10%)
In patients with cervical radiculopathy the MCID has to be over 7 points of change ( 14%) . When a decrease in score occurs the patients disabilities decrease so the patients situation improves.
MDC: the minimal detectable change (MDC), described as the amount of change that must be observed before the change can be considered to exceed the measurement error . In other words: Are the changes really caused by a changing of the patient or merely due to measurement errors?
There are some contradictions about the MDC for the NDI. The most common estimation is 5 out of 50 points or 10%. Other trains report higher MDC for patients with cervical radiculopathy : 13.4 points out of 50 or 26.8%.
The NDI appears to have good responsiveness in measuring neck pain and disabilities in patients with neck pain due to acute or chronic conditions as well as patients suffering from musculoskeletal dysfunctions, whiplash associated disorders and cervical radiculopathy 
The neck disability Index does not include psychosocial and emotional aspects of neck disabilities although these are very common in chronic neck pain ,whiplash associated disorders and Cervical Radiculopathy. These psychosocial and emotional (Biopsychosocial) aspects can be identified by the problem elicitation technique PET:
There are no valid benchmarks of the NDI.
Recent Related Research (from Pubmed)
- Macdermid JC, Walton DM, Avery S, Blanchard A, Etruw E, McAlpine C, Goldsmith CH. Measurement properties of the neck disability index a sustematic review Journal of Orthopedic and Sports Physical Therapy. 2009 May;39(5):400-17.
- Vernon H, Mior S. The neck disability index: A study of reliability and validity. Journal of Manipulative and Physiological Therapeutics, 1991, 14:409-15
- Riddle DL, Stratford PW. Use of generic versus region specific functional status measures on patients with cervical spine disorders. Physical Therapy, 1998;78:951-963
- Stratford PW, Riddle DL, Binkley JM et al (1999) Using the neck disability index to make decisions concerning individual patients Physiotherapy Canada, 2,107-112
- Cleland JA, Childs JD, Whitman JM.. Psychometric Properties of the Neck Disability Index and Numeric Pain Rating Scale in patients With Mechanical Neck Pain, Arch Phys Med Rehabil. 2008; 89(1):69-74
- Young IA, Cleland JA, Michener LA, Brown C. Reliability, Construct Validity, and Responsiveness of the Neck Disability Index, Patient-Specific Functional Scale, and Numeric Pain Rating Scale in Patients with Cervical Radiculopathy, American Journal of Physical Medicine & Rehabilitation, 2010; ;89(10):831-839
- Jan lucas hoving, Elizabeth F o’leary, ken r niere, sally green, Rachelle buchbinder, Validity of the neck disability index, Northwick park neck pain questionnaire, and problem elicitation technique for measuring disability associated with whiplash-associated disorders, pain,2003;102(3); 273-281
- Young BA, Walker MJ, Strunce JB, Boyles RE, Whitman JM, Childs JD. Responsiveness of the Neck Disability Index in patients with mechanical neck disorders. Spine, 2009 Jul 24, online article ahead of print.