VAS: Visual Analogue Scale for Assessing Subjective Sensations

VAS stands for Visual Analogue Scale, a measurement tool used in medicine and research: a straight line, usually 100 mm long, with a label at each end, such as "No pain" and "Worst imaginable pain". The patient marks a point on the line, and the score is the distance in millimeters from the left end, from 0 to 100.

It is used for sensations that can't be measured directly: pain, fatigue, nausea, anxiety, hunger or overall health. In US spelling it is the visual analog scale. In telecom and business, VAS also stands for value-added services, which is unrelated.

How a VAS works

1. The patient sees a horizontal line, usually 100 mm, with a short label at each end and no numbers or marks in between.
2. The instruction names the sensation and the time frame: "Mark the line to show how much pain you have right now."
3. The patient makes a vertical mark across the line.
4. The clinician measures the distance from the left end to the mark with a ruler. A mark at 62 mm is a score of 62.

Because there are no categories, the scale can pick up small changes, which is why it is common in clinical trials that compare symptoms before and after treatment.

VAS examples

A well-known variant is the EQ-VAS, part of the EuroQol EQ-5D health questionnaire: a vertical scale from 0 ("the worst health you can imagine") to 100 ("the best health you can imagine") on which people rate their health today.

How to read VAS scores

For pain, a commonly cited guide from a reanalysis of postoperative pain trials (Jensen, Chen and Brugger, 2003) is:

Example: a patient marks 62 mm before treatment and 28 mm after. The change is −34 mm, from moderate to mild pain. For a group, report the mean or median at each time point and the mean change.

These bands come from pain research. For other sensations, compare scores over time for the same person or between groups, rather than labeling a single score.

VAS vs numeric and verbal rating scales

A VAS is a continuous rating scale, while a Likert scale measures agreement in categories.

Common mistakes

• Photocopying the form. Copiers can shrink or stretch the line so it is no longer 100 mm, and the scores shift. Check the line length on every printed batch.
• Adding numbers or tick marks. The scale then works like a numeric scale, and people cluster on the marks.
• No time frame in the instruction: "now", "today" and "over the past week" give different answers.
• Comparing VAS and NRS scores as if they were the same. A 60 mm VAS and a 6 out of 10 are not guaranteed to match.
• Showing the previous score when measuring change. People anchor on it.

How to use a VAS in an online survey

On screen, a VAS becomes a slider from 0 to 100:

• Put the two anchor labels in the question so people know what each end means.
• If your tool allows it, hide the number while people drag, so the slider stays a visual scale.
• Be aware that a handle that starts in the middle can pull answers toward 50.
• For repeated measurements, pass a patient or participant code in the link so each person's scores can be matched over time.

In SurveyNinja, a Slider question takes whole numbers in the range you set, 0 to 100 by default, so a 0–100 VAS fits it directly. See Opinion Scale and Slider.