Visual Analog Scales

Visual Analog Scale (VAS) is a type of psychometric scale that uses a continuous measurement indicator rather than the multiple discrete indicators more common in many other types of measurement scales. Respondents to VAS make a subjective judgment on where their answer lies on a continuum and then mark their response on a VAS line. The VAS tends to be used to measure the same kinds of psychological phenomena that traditional rating scales are used to measure, such as mood, satisfaction, well-being, or psychological pain. For instance, respondents may be shown a horizontal line and asked to mark on the line their level of pain, where the left-most point represents no pain and the right-most point represents extreme pain. Researchers can then use the continuous distance between the mark and an end point as a subjective indicator of pain. In contrast, discrete scales, such as rating scales, will ask respondents a similar question, but with response options broken up into discrete points, which then serve as the subjective indicator of pain.

The continuous nature of measurement of the VAS allows respondents to potentially provide more precise answers and for a finer distinction between subjective states than traditional rating scales allow. Because traditional rating scales constrain respondents to predetermined ratings, such as 1–7, and because most psychological phenomena, such as pain or mood, have no objectively discrete intervals, the VAS should have an advantage over traditional rating scales in that it allows for the maximum possible distinction, limited only by the physical width of the response mark itself. This entry briefly reviews the administration and scoring of the VAS and then discusses variations in the VAS.

Variations

Types of VAS

There are generally three separate types of VAS: the traditional VAS, the Graphic Rating Scale (GRS), and the Numeric Rating Scale (NRS; see Figure 1 for samples of each type). The GRS is a form of the VAS where descriptor labels, such as “mild,” “moderate,” and “severe,” are placed at appropriate intervals on the evaluation line. The GRS may help participants more easily recognize where to mark their position on the evaluation line. However, the position of descriptor labels on the evaluation line can influence the distribution of ratings, so care should be taken when using the GRS.

Figure 1 The Visual Analog Scale, Graphic Rating Scale, and (Numeric) Rating Scale.

The NRS is often categorized as a type of VAS, but much more closely resembles a rating scale in that it does not use a continuous response line, but rather a line with discrete numbers representing equal intervals. Similar to rating scales, respondents select, or otherwise indicate, the number that [Page 1797]best matches their response to the question. Indeed, the NRS shares more common elements with traditional rating scales than the VAS, and comparisons between the NRS and the VAS should be seen as comparisons between rating scales and the VAS.

...