NDI: Neck Disability Index

What is NDI?

NDI (Neck Disability Index) is a validated clinical instrument used to assess self-reported neck-pain functional disability. The instrument contains 10 items.

Source / attribution: Vernon H, Mior S. The Neck Disability Index. J Manipulative Physiol Ther. 1991;14(7):409-415.

Clinical context: when NDI is used

The instrument's primary construct — self-reported neck-pain functional disability — is operationalized through a fixed set of items, each with a defined response format. This standardisation is what allows NDI scores to be compared meaningfully across clinicians, sites, and studies.

Like all screening or assessment instruments, NDI is a structured aid — not a diagnostic test in isolation. Results should be interpreted alongside history, examination, and clinical context. Where a score crosses an actionable threshold, the next step is typically a more detailed clinical evaluation rather than a definitive diagnosis.

Score NDI

Each item is scored on a 6-point scale (0–5). Your score updates live as you answer.

All scoring runs in your browser. No data is sent anywhere — close the tab and the answers are gone.

How NDI is scored

NDI uses simple summation: each item's selected response is converted to a numeric value, and the values are added to produce a total score. Reverse-scored items are inverted before summation.

Scoring notes: Multiply raw score by 2 to get the conventional NDI percentage.

NDI score interpretation

The cutoffs below are drawn from the published validation literature. Always interpret in clinical context.

How to score NDI: a step-by-step worked example

This is an illustrative walkthrough, not a real patient. Follow the same four steps with your own answers — or use the live calculator at the top of this page.

Step 1 — Score each item

Read each question and choose the response that best fits. Each response has a number next to it — that number is the item's score. The example below uses illustrative answers.

Step 2 — Add up the scores

Add up all the item scores you noted in Step 1.

1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 10

Step 3 — Look up the band

Find the row in the interpretation table whose range contains your total:

Total = 10 falls between 5 and 14 → Mild disability (10–28%)

Step 4 — What does this mean clinically?

Mild disability (10–28%). Pain moderately affects daily activities; consider conservative care.

A score is one input alongside history and examination. NDI supports clinical judgment — it does not replace it.

Score NDI with your own answers above →

Limitations & common pitfalls

• Multiply raw score by 2 to get the conventional NDI percentage.
• Screening, not diagnosis. A positive NDI score is not equivalent to a diagnosis. Confirmatory clinical evaluation is required before treatment decisions.
• Population calibration. Cutoffs were derived from specific validation populations. Performance can differ in other age groups, languages, comorbid conditions, or clinical settings.
• Self-report bias. Patient-reported instruments are subject to under- and over-reporting; clinical context is essential.
• Comprehension and literacy. Item phrasing assumes baseline reading comprehension; consider clinician-administered alternatives where literacy or language barriers exist.

How NDI compares to other orthopaedics scales

If NDI doesn't fit your context, related instruments in orthopaedics include:

Frequently asked questions about NDI

References & validation

NDI is supported by the following peer-reviewed sources:

• Vernon H, Mior S. The Neck Disability Index. J Manipulative Physiol Ther. 1991;14(7):409-415.