Concept Architecture
Concept
Theoretically, the Visual Analogue Scale (VAS) is a psychometric and preference-elicitation instrument in which respondents indicate the perceived intensity or value of a health state on a continuous line bounded by defined endpoints. It is grounded in measurement theory and assumes that the respondent?s position on the line represents an ordered, approximately interval-scaled judgement. In health economics, the VAS is used to measure symptoms, self-rated health and direct valuations of health states.
Mathematically, the VAS response is represented by the distance between the lower endpoint and the respondent?s mark, usually transformed onto a standard scale such as 0 to 100 or 0 to 1. Rescaling is performed using a linear transformation. When used for health-state valuation, VAS scores represent cardinal ratings but are not choice-based utilities under expected utility theory.
In practice, respondents mark a point on a horizontal or vertical line anchored by states such as worst imaginable health and best imaginable health. The mark is measured electronically or as a physical distance from the lower anchor. VAS scores are used in clinical outcome assessment, health-status monitoring and supplementary health-state valuation, although choice-based methods are generally preferred for generating utilities used in quality-adjusted life-year calculations.
Purpose
Used to obtain a continuous rating of symptom severity, perceived health or health-state value by recording a respondent?s position between defined endpoint anchors.
Mathematical Formulae
Primary Formula
VAS Score = d / L ? 100
where:
- d = distance from the lower anchor to the respondent?s mark
- L = total line length
Supporting Formulae
Rescaling from 0?100 to 0?1:
VAS??? = VAS????? / 100
Change in VAS score:
?VAS = VAS? ? VAS?
Standardised VAS change:
ES = ?VAS? / SD?
Related Mathematical Methods
- Rating Scale
- Health-State Valuation
- Responsiveness Analysis
- Effect Size
- Standardised Response Mean
- Preference Elicitation
Example
A patient marks a pain VAS 32 mm from the lower endpoint on a 100 mm line.
VAS Score = 32 / 100 ? 100 = 32
Following treatment, the mark is 14 mm from the lower endpoint.
?VAS = 14 ? 32 = ?18
The negative change indicates an 18-point reduction in reported pain severity.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| PRODUCT | =B2/C2*100 | Converts measured distance into a 0?100 VAS score. |
| ROUND | =ROUND(B2/C2*100,1) | Reports the VAS score to one decimal place. |
| LET | =LET(Distance,B2,Length,C2,Distance/Length*100) | Calculates a standardised VAS score. |
| AVERAGE | =AVERAGE(D2:D101) | Calculates the mean VAS score for a study group. |
| STDEV.S | =STDEV.S(D2:D101) | Estimates variability in VAS responses. |
VBA (Optional)
VBA can automate transformation, validation and longitudinal analysis of visual analogue scale responses across patients and assessment periods.
Sources
- Torrance GW, Feeny D, Furlong W. Visual analog scales: do they have a role in the measurement of preferences for health states? Medical Decision Making.
- McCormack HM, Horne DJL, Sheather S. Clinical applications of visual analogue scales: a critical review. Psychological Medicine.
- Brazier J, Ratcliffe J, Salomon JA, Tsuchiya A. Measuring and Valuing Health Benefits for Economic Evaluation. Oxford University Press.
- Fayers PM, Machin D. Quality of Life: The Assessment, Analysis and Reporting of Patient-Reported Outcomes. Wiley.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes. Oxford University Press.
Related Concepts (2)
Library
Publications
1
Measuring and Valuing Health Benefits for Economic Evaluation — Brazier, Ratcliffe, Salomon & Tsuchiya, 2nd Edition ed., 2017 (Oxford University Press)
The comprehensive text on the measurement and valuation of health benefits for economic evaluation — defining health, valuation techniques (time trade-off, standard gamble), whose values to use, preference-based measures (EQ-5D, SF-6D), and the construction of QALYs.
BookView source →
Frequently Asked Questions (6)
What is a visual analogue scale?
A health state valuation method in which respondents mark a perceived health state on a continuous line anchored between worst and best imaginable health.
Source: Torrance GW. Measurement of health state utilities for economic appraisal. Journal of Health Economics. 1986;5(1):1-30. doi:10.1016/0167-6296(86)90020-2.
Why are visual analogue scale values not treated as utilities directly?
A mark on a rating line records how a respondent feels about a state but involves no choice in which something is given up, so the resulting number lacks the trade-off meaning that quality-adjusted life years require. Respondents also tend to avoid the ends of the line and to space their marks in ways that reflect the scale's format as much as their preferences. For these reasons values from the scale are usually transformed, or used only as an input to a choice-based method, rather than taken as utilities. Brazier and colleagues (2007) explain this reservation.
Source: Brazier et al. 2007
How does a visual analogue scale work?
The respondent is shown a line, often marked from zero at the worst imaginable health to one hundred at the best, and asked to place each health state at the point reflecting its desirability. The distance of the mark from the endpoints gives the state's value on the scale. With the endpoints anchored to death and full health, the readings can be converted toward utilities, though they are treated as preliminary rather than final.
Source: Torrance 1986
What are the advantages of a visual analogue scale?
The visual analogue scale is quick, simple, and easy for respondents, requiring only that they place states on a line rather than reason about risk or trade time, so it imposes little burden and can value many states. It gives a continuous measure of relative desirability and is inexpensive to administer. These features make it widely used, often to obtain an initial valuation alongside choice-based methods, and the EQ-5D includes such a scale for overall health.
Source: Torrance 1986
What are the limitations of a visual analogue scale?
Because it involves no trade-off or choice under risk, the visual analogue scale may not yield utilities in the sense economic evaluation requires, and its values differ systematically from choice-based ones, often clustering away from the extremes and toward the middle. Respondents may use the scale inconsistently or space states unevenly. For these reasons its values are frequently transformed or treated as preliminary rather than as definitive utilities.
Source: Torrance 1986
How are visual analogue scale values used?
Visual analogue scale values are used to describe the relative desirability of health states and, after transformation, as approximate utilities, though because they differ from choice-based values they are often converted using an empirical relationship before use in quality-adjusted life years. The scale is also used to record overall self-rated health, as in the EQ-5D. Its readings serve as a simple valuation, usually complemented or adjusted by choice-based methods for economic evaluation.
Source: Torrance 1986
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British health economist
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