Pain scales: NPRS and VAS

What a pain scale measures

Both scales measure one thing: how intense the pain is. Hawker and colleagues (2011), in their review of adult pain measures, describe the VAS and the numeric rating scale as unidimensional measures of pain intensity. A score will not tell you where the pain is, what it feels like or how much it stops the patient from doing. If you need that, add a function measure.

The NPRS goes by several names. Hawker and colleagues call it the Numeric Rating Scale for pain (NRS Pain), the IMMPACT group writes "0 to 10 numerical rating scale", and Childs and colleagues (2005) use "numeric pain rating scale". All of them mean the same 11-point scale. The VAS is also spelled visual analogue scale.

How to use the numeric pain rating scale (NPRS)

The patient chooses the whole number from 0 to 10 that best describes the intensity of their pain. Hawker's review gives the usual anchors: 0 is "no pain", and 10 is "pain as bad as you can imagine" or "worst pain imaginable". The scale is usually shown as a horizontal bar or line with the numbers on it.

You can ask it out loud, so it also works over the telephone, or hand it over on paper. It takes under a minute. A typical question is: "On a scale from 0 to 10, where 0 is no pain and 10 is pain as bad as you can imagine, how would you rate your pain on average over the last 24 hours?"

Pick a recall period and keep it at every visit. Hawker's review lists pain in the last 24 hours and average pain as the most common. Pain right now and the worst pain of the day are different questions, so do not compare a score for one with a score for the other.

Record the number with the recall period, for example "NPRS 6/10, average pain over the last 24 hours". If you use different anchor words, write them down too. A higher number means more intense pain. The review gives no cut points for mild, moderate or severe pain on the NRS, so we do not give any here.

NRS scores hold up well when you repeat the test. In patients with rheumatoid arthritis, test-retest correlation was 0.96 in literate and 0.95 in illiterate patients (Ferraz and colleagues, as reported by Hawker). Its correlation with the VAS in rheumatic and other chronic pain ranges from 0.86 to 0.95.

How to use the visual analog scale (VAS)

The pain VAS is a line, usually 10 cm (100 mm) long, drawn horizontally or vertically, with a word anchor at each end. For pain intensity, the most common anchors are "no pain" at 0 and "pain as bad as it could be" or "worst imaginable pain" at 100. Leave the rest of the line blank. Hawker and colleagues advise against numbers or words along it, because marks then tend to cluster around them.

1. Check the printed line measures exactly 100 mm. Hawker and colleagues warn that photocopying can change its length.
2. Give the patient the sheet and a pen. The VAS is filled in by the patient on paper. It cannot be given out loud or by telephone.
3. Ask them to draw a short line across the scale at the point that shows how intense their pain is, for the recall period you have chosen. For the VAS, the usual periods are pain now and pain in the last 24 hours.
4. Measure with a ruler, in millimeters, from the "no pain" end to the patient's mark. The score runs from 0 to 100.
5. Record the score in millimeters with the recall period, for example "VAS 45 mm, pain now".

Use the same orientation each time. Slightly lower scores have been reported on a horizontal line than on a vertical one, although the two correlate at 0.99. Older patients with cognitive impairment may find the VAS hard to understand, and staying with them while they fill it in may reduce errors.

Hawker and colleagues point out that the pain VAS has no normative values. The cut points below come from Jensen and colleagues (2003), who reanalyzed 2 trials of pain after surgery (123 and 125 patients after knee replacement, hysterectomy or laparoscopic myomectomy).

These bands describe how patients after surgery labeled their pain. They may not fit other patients, and they are not targets for treatment.

Repeat ratings are close but not identical. In rheumatoid arthritis, test-retest correlation was 0.94 in literate patients and 0.71 in illiterate patients (Ferraz and colleagues, as reported by Hawker). Bijur and colleagues (2001) asked adults with acute pain in 2 emergency departments for 2 VAS ratings 1 minute apart. Half of the pairs were within 2 mm of each other, 90% within 9 mm and 95% within 16 mm. Ratings repeated best at the extremes of pain and least well in the moderate range.

NPRS or VAS: which pain scale should you use?

Hjermstad and colleagues (2011) reviewed 54 studies that compared numeric, verbal and visual analog pain scales in adults. In 15 of the 19 studies that reported it, patients completed the numeric scale more often than the VAS or verbal scale. Eleven studies recommended the numeric scale, for its higher completion rates, better responsiveness and ease of use; 29 gave no preference. NRS and VAS scores mostly matched, but a few studies found VAS scores that were consistently higher.

Hawker and colleagues also report that people with chronic pain prefer the NRS over the VAS because it is easier to understand and complete. It works by phone too, and it is simpler to score.

Whichever you choose, stay with it for that patient. The review found 24 different anchor phrases in use, 15 of them for numeric scales, and scores from the two scales do not always match. A change from a VAS reading to an NPRS reading is not a reliable change in pain.

Faces pain scale for children (FPS-R)

The Faces Pain Scale Revised (FPS-R) is a pain scale for children, made of six drawn faces. Hicks and colleagues (2001) cut the original Faces Pain Scale from seven faces to six so that it scores on the common 0 to 10 metric. They found it suitable for children's acute pain from age 4 or 5 onward. The International Association for the Study of Pain (IASP) says the scale shows a close linear relationship with visual analog pain scales across ages 4 to 16.

The IASP instructions score the chosen face 0, 2, 4, 6, 8 or 10, counting left to right, so 0 equals "No pain" and 10 equals "Very much pain". They ask you not to use words like "happy" and "sad", because the scale is meant to measure how children feel inside, not how their face looks.

We do not show the faces on this page. The IASP allows free clinical, educational and research use of the FPS-R without asking, as long as the scale is not modified, but reproducing it in a journal, a book or on a web page needs permission from Mapi Research Trust. The IASP FPS-R page gives the instructions and links to Mapi Research Trust, where you get the scale itself by completing a license agreement.

Minimal clinically important difference for the NPRS

Tashjian and colleagues (2009) define the MCID as "the smallest difference in an outcome score which a patient perceives as beneficial". The first three studies below found it by comparing the change in pain score with how much better patients said they felt (in the Childs study, the patient's and the therapist's ratings averaged). The IMMPACT figures are consensus benchmarks drawn from studies like these.

Farrar and colleagues linked the change in daily pain diary scores to the patient global impression of change. The link held regardless of study, disease, age, sex or treatment group. The IMMPACT report adds from the same data that drops of 4 points or more, or 50% or more, matched "very much improved", and that a drop of at least 1.7 points or 28% best separated "much improved" from smaller changes.

The starting score matters too. Farrar and colleagues found that the percentage change needed stayed consistent whatever the baseline, while higher baseline scores needed larger changes in points. Salaffi and colleagues found that patients with high baseline pain (above 7) showed bigger changes in both points and percent at each level of improvement than patients with low baseline pain (below 4).

Childs and colleagues also looked at measurement error. The standard error of measurement was 1.02 points, which gives a minimal detectable change of 2 points. They concluded that a 2-point change on the NPRS is clinically meaningful and exceeds measurement error in low back pain.

The IMMPACT group called its percentages provisional. They still need confirming, and the report says the change that matters may depend on baseline pain, age, the clinical condition and earlier response to treatment.

Minimal clinically important difference for the VAS

Hawker and colleagues quote the Tashjian figure as 1.37 cm; the paper's abstract rounds it to 1.4 cm. Jensen and colleagues found that percentage change was less affected by the starting pain level than change in millimeters. Across VAS and NRS studies, the IMMPACT report found that drops of about 1 cm (or 1 point) or 15 to 20% reflected minimal change, while drops of 2.0 to 2.7 points or 30 to 41% meant more to patients.

How to read a change in pain score

The calculator takes the change as baseline minus follow-up, so a positive number means less pain. Percentage change is that difference divided by the baseline score, times 100. It cannot be worked out when the baseline is 0.

A low baseline makes the percentage look large. A drop from 1 to 0 on the NPRS is a 100% reduction, yet it is only 1 point, which is inside measurement error. Salaffi and colleagues also found that the change that matters is not the same along the whole scale. The calculator adds a note when the NPRS baseline is below 4 or the VAS baseline is below 45 mm; judge the change in points or millimeters first in that case.

Check the change against measurement error first. Childs and colleagues found a minimal detectable change of 2 points on the NPRS in low back pain. On the VAS, 95% of repeat ratings from adults with acute pain in the Bijur study were within 16 mm of each other a minute apart, so a change of 16 mm or less may be noise. Ratings taken a minute apart leave out the natural change in pain from day to day, so the noise between visits is likely to be larger.

Every MCID above is an average from one group of patients with one condition, measured one way. Use it to help judge a change. On its own, it does not show whether treatment worked for the patient in front of you. Ask the patient how they feel their pain has changed, and look at what they can do, alongside the score.

A rise in pain needs its own judgment. Most thresholds here come from improvement, and the IMMPACT report notes that the change that matters for getting worse may differ from the change that matters for getting better.

Limits of the NPRS and VAS

• They rate intensity only. Hawker and colleagues note that neither scale captures the complexity of the pain experience. In focus groups, people with chronic back pain or hip and knee osteoarthritis said the NRS did not capture improvements when their symptoms fluctuate.
• The VAS needs a printed line and a pen, and it cannot be done by phone. Older patients with cognitive or motor problems may struggle with it, and it takes more work to score than the NRS.
• Literacy matters for the VAS. In the rheumatoid arthritis data reported by Hawker, VAS test-retest correlation dropped to 0.71 in illiterate patients, while the NRS stayed at 0.95.
• Anchors and recall periods vary between clinics and studies. Hjermstad and colleagues found 24 different anchor phrases, and whether they change the scores has not been tested.
• MCID values differ between studies, as the tables show. Use the one closest to your patient, and say which one you used when you report a change.

If you are a patient and your pain is severe, new or getting worse, see a doctor or physiotherapist instead of only tracking it on a scale.

References

1. Hawker GA, Mian S, Kendzerska T, French M. Measures of adult pain: Visual Analog Scale for Pain (VAS Pain), Numeric Rating Scale for Pain (NRS Pain), McGill Pain Questionnaire (MPQ), Short-Form McGill Pain Questionnaire (SF-MPQ), Chronic Pain Grade Scale (CPGS), Short Form-36 Bodily Pain Scale (SF-36 BPS), and Measure of Intermittent and Constant Osteoarthritis Pain (ICOAP). Arthritis Care and Research. 2011;63(S11):S240-S252. doi:10.1002/acr.20543
2. Farrar JT, Young JP Jr, LaMoreaux L, et al. Clinical importance of changes in chronic pain intensity measured on an 11-point numerical pain rating scale. Pain. 2001;94(2):149-158. doi:10.1016/S0304-3959(01)00349-9
3. Salaffi F, Stancati A, Silvestri CA, Ciapetti A, Grassi W. Minimal clinically important changes in chronic musculoskeletal pain intensity measured on a numerical rating scale. European Journal of Pain. 2004;8(4):283-291. doi:10.1016/j.ejpain.2003.09.004
4. Childs JD, Piva SR, Fritz JM. Responsiveness of the numeric pain rating scale in patients with low back pain. Spine. 2005;30(11):1331-1334. doi:10.1097/01.brs.0000164099.92112.29
5. Dworkin RH, Turk DC, Wyrwich KW, et al. Interpreting the clinical importance of treatment outcomes in chronic pain clinical trials: IMMPACT recommendations. Journal of Pain. 2008;9(2):105-121. doi:10.1016/j.jpain.2007.09.005
6. Hjermstad MJ, Fayers PM, Haugen DF, et al. Studies comparing numerical rating scales, verbal rating scales, and visual analogue scales for assessment of pain intensity in adults: a systematic literature review. Journal of Pain and Symptom Management. 2011;41(6):1073-1093. doi:10.1016/j.jpainsymman.2010.08.016
7. Jensen MP, Chen C, Brugger AM. Interpretation of visual analog scale ratings and change scores: a reanalysis of two clinical trials of postoperative pain. Journal of Pain. 2003;4(7):407-414. doi:10.1016/S1526-5900(03)00716-8
8. Kelly AM. The minimum clinically significant difference in visual analogue scale pain score does not differ with severity of pain. Emergency Medicine Journal. 2001;18(3):205-207. doi:10.1136/emj.18.3.205
9. Kelly AM. Setting the benchmark for research in the management of acute pain in emergency departments. Emergency Medicine. 2001;13(1):57-60. doi:10.1046/j.1442-2026.2001.00179.x
10. Tashjian RZ, Deloach J, Porucznik CA, Powell AP. Minimal clinically important differences (MCID) and patient acceptable symptomatic state (PASS) for visual analog scales (VAS) measuring pain in patients treated for rotator cuff disease. Journal of Shoulder and Elbow Surgery. 2009;18(6):927-932. doi:10.1016/j.jse.2009.03.021
11. Wolfe F, Michaud K. Assessment of pain in rheumatoid arthritis: minimal clinically significant difference, predictors, and the effect of anti-tumor necrosis factor therapy. Journal of Rheumatology. 2007;34(8):1674-1683. PubMed 17611989
12. Bijur PE, Silver W, Gallagher EJ. Reliability of the visual analog scale for measurement of acute pain. Academic Emergency Medicine. 2001;8(12):1153-1157. doi:10.1111/j.1553-2712.2001.tb01132.x
13. Hicks CL, von Baeyer CL, Spafford PA, van Korlaar I, Goodenough B. The Faces Pain Scale-Revised: toward a common metric in pediatric pain measurement. Pain. 2001;93(2):173-183. doi:10.1016/S0304-3959(01)00314-1
14. International Association for the Study of Pain. Faces Pain Scale Revised (FPS-R). iasp-pain.org

This tool compares a change in pain score with published thresholds for education. It is not a medical assessment.