A simple method for turning subjective experiences into numerical data
Pain, pleasantness, fatigue, irritation, and other subjective experiences can feel clear to the person experiencing them, but they cannot always be measured directly in the same way as body temperature or blood pressure.
A Visual Analog Scale, commonly abbreviated as VAS, is a method used to record these subjective experiences. The respondent indicates their answer by marking a position along a continuous line, and that position is then converted into a numerical value.
VAS measures are widely used in medicine, psychology, physiology, human factors research, sensory evaluation, and many other fields.
The term is also spelled Visual Analogue Scale, particularly in British English. Both spellings refer to the same general measurement method.
How does a Visual Analog Scale work?
A typical VAS consists of a straight line with labels describing the minimum and maximum ends of the experience being measured.
For example, a pain scale might appear as follows:
Example rVAS response screen, showing a scale from 'no pain at all' to 'worst pain'
The respondent marks the point on the line that best represents their current experience.
Traditional paper-based VAS measures commonly use a 100 mm, or 10 cm, line. After the respondent makes a mark, the researcher measures the distance from the left endpoint to the marked position. The result can then be recorded as a value from 0 to 100.
For example, if the mark is placed 72 mm from the left endpoint, the VAS value is recorded as 72.
What can a VAS measure?
VAS measures are often associated with pain assessment, but they are not limited to pain.
By changing the question and endpoint labels, a VAS can be used to assess many different subjective experiences, including:
- pain or discomfort
- fatigue or sleepiness
- pleasantness
- perceived intensity
- breathlessness
- anxiety or tension
- satisfaction
- taste or odor perception
- ease of use
- impressions of a product or environment
However, simply presenting a line does not automatically create a valid measurement.
The question, endpoint labels, target population, timing, and administration procedure must all match the concept being assessed. The validity and reliability of a scale should therefore be considered in relation to its specific purpose and study population.
How is a VAS different from an NRS or a Likert scale?
Several types of scales can be used to record subjective experiences.
Numerical Rating Scale
A Numerical Rating Scale, or NRS, asks the respondent to choose from a predefined set of numbers, such as 0 to 10.
Likert scale
A Likert-type scale asks the respondent to select from a series of categories, such as: strongly disagree, disagree, neither agree nor disagree, agree, strongly agree.
Visual Analog Scale
A VAS allows the respondent to choose any position along a continuous line rather than selecting a predefined number or category.
For example, a respondent may feel that a rating of 6 is too low but a rating of 7 is too high. A VAS allows them to place their response between those values. This continuous response format is one of the main characteristics of the Visual Analog Scale. VAS, NRS, and Likert-type scales are not interchangeable in every situation. The most appropriate format depends on the purpose of the study, the target population, and the type of experience being measured.
Advantages of using a VAS
It can capture small differences
Because respondents can select any position along the line, a VAS can record subtle differences that may be difficult to represent using only a small number of categories.
The response method is simple
The basic task is straightforward: mark the position that best represents the current experience. When the question and endpoint labels are clear, respondents can usually complete the assessment quickly.
It is suitable for repeated measurements
The same scale can be administered before and after an intervention, following different stimuli, or across multiple experimental conditions. This makes VAS measures useful for assessing changes within a participant and differences between conditions.
It can be adapted to many research fields
VAS measures are not specific to a single disease, symptom, or discipline. With appropriate wording and study design, they can be used in clinical research, psychology, physiology, sensory research, driving studies, usability testing, product evaluation, and many other fields.
Important considerations when using a VAS
Endpoint labels define what is being measured
A scale ranging from "not unpleasant" to "extremely unpleasant" does not measure exactly the same concept as a scale ranging from "extremely pleasant" to "extremely unpleasant."
Questions and endpoint labels should clearly tell respondents what they are being asked to evaluate.
Measurement conditions should remain consistent
Changes in line length, orientation, wording, input method, or numerical display may influence responses. Within a study, the same presentation and administration procedure should therefore be used whenever possible.
The recall period should be clear
"Pain right now" and "average pain during the past week" require different judgments. Longer recall periods may also be influenced more strongly by memory. Researchers should clearly specify whether the participant should evaluate the present moment, the period immediately after a stimulus, the past 24 hours, or another defined interval.
A VAS value does not have a universal meaning
A score of 30 does not automatically mean "mild," "normal," or "abnormal."
The meaning of a value depends on the question, population, condition, and study design. A VAS is a method for recording subjective responses numerically; it does not independently provide a diagnosis or treatment decision.
Accessibility and usability should be considered
Some participants may have difficulty understanding or accurately marking a continuous line because of visual, motor, cognitive, or other limitations. Researchers should confirm that the intended participants can understand and operate the scale before beginning data collection.
Paper and digital Visual Analog Scales
With a traditional paper VAS, the researcher must usually measure each response with a ruler and manually enter the result into a spreadsheet or database.
A digital VAS can automatically convert the selected position into a numerical value. This can reduce the work required for:
- measuring response positions
- manually entering values
- combining repeated responses
- matching results with participant IDs and conditions
- preparing data files for analysis
Studies comparing electronic and paper VAS administration have generally reported close agreement when the electronic scale is designed and administered appropriately.
However, displaying a slider on a screen does not automatically make it equivalent to a paper VAS.
Researchers should consider factors such as:
- the physical and visual length of the scale
- whether an initial marker position is displayed
- whether the current numerical value is visible
- how responses are entered
- whether the endpoints can be selected accurately
- whether the same device and procedure are used throughout the study
Consistency of measurement remains important regardless of whether the scale is presented on paper or digitally.
Using rVAS for Visual Analog Scale research
rVAS is an iPad application designed to create, administer, record, and export Visual Analog Scale measurements for research and survey use.
Participants respond by drawing a mark with a finger, Apple Pencil, or compatible stylus, similar to marking a paper VAS. The response position is automatically converted into a VAS value.
Researchers can configure:
- multiple VAS questions
- multiple conditions or stimuli
- repeated measurements
- presentation-order patterns
- participant-specific pattern assignments
Results from multiple participants, conditions, and questions can be combined and exported in XLSX format for further analysis.
rVAS is designed around local data storage and can be used without a continuous internet connection.
rVAS is not a medical device and is not intended to diagnose disease, recommend treatment, or make clinical decisions. It is a research-support tool for recording subjective evaluations and managing study data.
Researchers remain responsible for selecting appropriate questions, endpoint labels, administration procedures, and analysis methods for their study.
Summary
A Visual Analog Scale is a simple method for converting subjective experiences into numerical data.
Respondents indicate their experience by marking a position along a continuous line. That position can then be measured or digitally converted into a value.
Although the format is simple, reliable use requires careful attention to:
- the question being asked
- the endpoint labels
- the recall period
- the administration procedure
- the target population
- the consistency of the scale format
When appropriately designed and administered, VAS measures can be used to record pain, pleasantness, fatigue, perceived intensity, satisfaction, and many other subjective experiences across a wide range of research fields.
References
- Aitken RCB. “Measurement of feelings using visual analogue scales.” Proceedings of the Royal Society of Medicine, 1969. https://doi.org/10.1177/003591576906201005
- U.S. Food and Drug Administration. “Guidance for Industry: Patient-Reported Outcome Measures—Use in Medical Product Development to Support Labeling Claims.” U.S. Food and Drug Administration, 2009.
- Jamison RN, Gracely RH, Raymond SA, et al. “Comparative study of electronic vs. paper VAS ratings: a randomized, crossover trial using healthy volunteers.” Pain, 2002. https://doi.org/10.1016/S0304-3959(02)00178-1
- Byrom B, Elash CA, Eremenco S, et al. “Measurement comparability of electronic and paper administration of Visual Analogue Scales: a review of published studies.” Therapeutic Innovation & Regulatory Science, 2022. https://doi.org/10.1007/s43441-022-00376-2
