Visual Analog Survey Scale — A Pain-ful Misnamed Scale

Visual Analog Scale –

A Pain-ful Misnamed Scale

Visual Analog Scales were created for use in hospital emergency rooms to assess pain from patients where language skills can’t be assumed.

Unfortunately, it’s been amended – you could say corrupted – such that the scale is not analog (continuous) and not really a visual scale.

A friend recently had a medical condition that required EMT (Emergency Medical Technician) response. The lead person asked my friend, who was flat on his back, “How much pain are you in where one means no pain and 10 is the worst pain you’ve ever experienced.” That oral presentation was based upon the commonly used Visual Analog Scale (VAS) for pain assessment.

We’ll look at the evolution of the Visual Analog Pain Scale in the context of how measurement scales are presented to the respondent.

A True Visual Analog Scale

Frederick C. Van Bennekom

How to Present the Survey Scale

In the surveying process, we typically use lots of scalar questions. You know, those 1-to-10 questions… We hope that they are interval rating scale questions, but that’s a separate discussion. At worst, they’re ordinal scale questions.

The survey designer must decide how to present the scale to the respondent – a critical survey design decision.

The surveyor has five different options for presenting the scale:

Verbally: with words, whether spoken or written that describe some ascending order, such as Not Satisfied to Very Satisfied. (In the vernacular, “verbal” means “spoken” but properly it means use of words.)
Numerically: with a numbered scale, such as a 1-to-5 or 1-to-10 scale.
Ideographically: with pictures, such as icons or emojis that display increasing emotions.
Visually: with a continuous line, marked with some low-to-high descriptors. (Personally, I prefer “Linear” as the term since ideographs are also “visual”.)
Color Coding: using colors to imply scale direction and level. So called traffic-light color coding schemes are typically used. Red = bad. Yellow = neutral. Green = good. This color scheme appears to be cross-cultural, but it does have limitations for color blind respondents.

Regardless of the presentation method, the respondent is asked to identify the place on the scale that best matches their views. The choice is coded with a number to measure whatever we’re trying to understand – the phenomenon of interest – such as degree of satisfaction or level of pain. The response could be coded with the verbal descriptors, but text is a hassle to analyze.

All four of these presentation methods can be administered on paper or webform, but only the Verbal and Numerical methods can be presented orally — in a telephone or personal interview.

Combination Survey Scales

Commonly, we use a combination of scale presentations. We’ve all seen or heard the verbal plus numeric scale presentation. (“On a scale from 1 to 10 where 1 represents Not Satisfied and 10 represents Very Satisfied…”) It’s probably the most common scale presentation approach.

In fact, numeric and visual scales must be combined with words or pictures that label or anchor the scale for the respondent. Numbers and lines have no inherent high-to-low designation. So, we must identify for the respondent which end of the scale is high and which is low. We can only do that with pictures or words.

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You might think that numbers do run low-to-high, but whether a 1 is high or low is driven by context and cultural factors. Many assume that a higher number represents “better.” But consider: have you ever heard fans at a sporting event cheer: “We’re number 10!”? Or a golfer being happier with a higher score?

Now consider this contrast:

Which is worse: 1st degree murder or 2nd degree murder?
- 1st, of course.
Which is worse: a 1st degree burn or 2nd degree burn?
- 2nd — with 3rd degree being the worst.

We’re just not consistent in the directionality of numbers. 10 (or 1) can be good or bad depending upon the context. Thus, verbal or ideographic labels are always needed when using a numeric scale presentation.

Commonly used Visual Analog Scale

A commonly used example of a Visual Analog Scale.

BoneAndSpine.com

Visual Analog Survey Scale

The Visual Analog Scale (VAS) is one such combination scale presentation, developed by Hayes and Patterson in 1921. It was created for use in hospitals where pain levels need to be assessed quickly with patients who might not understand the local language. So non-verbal scale descriptors are used such as color-coded smiley faces.

Here’s the concept. The patient is shown a sheet of paper with a 100 mm horizontal line where one end of the line represents no pain and the other end extreme pain. Ask the patient to indicate how much pain they’re feeling by marking a place along the line. The distance to the mark is measured, and voila, we have a measurement on a 0 to 100 scale.

Why is this “visual”? Visual is an odd term here. As mentioned above, “Linear” might be better. Arguably, ideographs are “visual.” The line as the “visual” representation of the scale makes this, well, visual. On a webform, it would be a slider, which are increasing in use in survey tools.
What makes this “analog”? Analog means “continuous” – as opposed to “discrete”. Verbal, numerical, and ideographic scale representations have distinct, individual points to the scale. For example: 1, 2, 3, 4 and 5. That makes these scale types discrete. (And I don’t mean “discreet”!) The longest discrete scale commonly used is a 0-to-10 scale – all of 11 points! — for the Net Promoter Score measurement.

A line (or slider) technically has an infinite number of points on it. That’s continuous or analog.

Why use an analog or visual scale? The argument for a visual scale: it’s more precise. Think about final exams in school. You likely were graded on a 100-point scale. An 89 (B+) was way different from an 91 (A-). So, the 100-point scale was a more precise reflection of your grasp of the material than a 10-point scale would be.

While an analog scale has an infinite number of points on it, whatever point the respondent chooses is usually coded as a 0-to-100 scale. While we could be more precise and measure to the 10^th of a millimeter, at some point we simply have “false precision”.

Visual Analog Scale with Wong-Baker facial ideographic scale.

Visual Analog Scale with Wong-Baker Facial Scale

The Evolution of the Visual Analog Survey Scale

Now, look at the commonly-used example of the Visual Analog Scale (VAS) shown nearby. (Run a search on “Visual Analog Scale images” and you’ll see more examples, most of whose provenance is hard to identify.) You might be thinking, “I see a line divided into 5 or 10 segments with hashmarks, coupled with smiley faces, color coding, and words. How does that jibe with your description?”

It doesn’t.

The VAS has been “improved” over the years – or bastardized if you prefer – to the point that “Visual Analog” is a truly misleading descriptor.

Is it Analog? The hash or tick marks along the horizontal line make the scale discrete rather than analog. Even though someone could mark a point anywhere along the line, research has shown that the presence of the marks leads respondents to select near those marks even with no instructions to do so.
Is it an Interval Scale? For a scale to be interval, there must be a consistent unit of measurement, that is, the difference between each pair of points on the scale must be the same. (Think of a ruler.) For the 2nd VAS example above, notice the descriptive terms used. Is the difference between Uncomfortable and Dreadful the same difference as Dreadful and Horrible? Not to me. Look at the 3 highest pain descriptors: Dreadful, Horrible, and Agonizing. Aren’t those effectively synonyms? And are they even ordinal? Print out the descriptors on individual cards and ask friends to put them in order. Think you’ll get consistent order? You won’t. If they’re not ordinal, they can’t be interval.
Is it Visual? Yes, it has the visual component of the horizontal line, albeit with hash marks, but the line has been “augmented” with verbal, numeric, and ideographic labeling.

So, many Visual Analog Scales’ proper name is the Visual Verbal Numeric Ideographic Discrete Scale (VVNIDS).

Now that’s a mouthful! But it is a better description of this measurement instrument. The current name grossly distorts the meaning of Visual and Analog. Just call them Pain Measurement Tools.

A Final Note About Provenance

As noted, the pain measurement scale has been around for a century. Scores of variations have been created, which have then been edited and “published”. Medical researchers have assessed the efficacy of them. Who owns the copyright? In most cases that’s tough, if not impossible, to discern. I’ve had inquiries to use the images I’ve used in this review, which is why I’ve added this note. For the latter two images I’ve included in hover text the source from which I got them.