Visual Analogue Scale

Original Editor - Venus Pagare

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Introduction

A Visual Analogue Scale (VAS) is a measurement instrument that tries to measure a characteristic or attitude that is believed to range across a continuum of values and cannot easily be directly measured. It is often used in epidemiologic and clinical research to measure the intensity or frequency of various symptoms. For example, the amount of pain that a patient feels ranges across a continuum from none to an extreme amount of pain. From the patient's perspective this spectrum appears continuous ± their pain does not take discrete jumps, as a categorization of none, mild, moderate and severe would suggest. It was to capture this idea of an underlying continuum that the VAS was devised.

Purpose

The pain VAS is a unidimensional measure of pain intensity, which has been widely used in diverse adult populations, including those with rheumatic diseases.    

Structure,Orientation and Response Options

VAS can be presented in a number of ways,including:

• scales with a middle point,graduations or numbers (numerical rating scales),
• meter-shaped scales (curvilinear analogue scales),
• "box-scales,"scales consisting of circles equidistant from each other(one of which the subject has to mark),and
• scales with descriptive terms at intervals along a line (graphic rating scales or Likert scales) 
• The most simple VAS is a straight horizontal line of fixed length, usually 100 mm. The ends are defined as the extreme limits of the parameter to be measured (symptom,pain,health) orientated from the left (worst) to the right (best). In some studies,horizontal scales are orientated from right to left ,and many investigators use vertical VAS.
• No difference between horizontal and vertical VAS has been shown in a survey involving 100 subjects but other authors have suggested that the two orientations differ with regard to the number of possible angles of view. Reproducibility has been shown to vary along a vertical 100-mm VAS and along a horizontal VAS . The choice of terms to define the anchors of a scale has also been described as important.
  

Administration

• They are generally completed by patients themselves but are sometimes used to elicit opinions from health professionals.
  
• The patient marks on the line the point that they feel represents their perception of their current state.
• The VAS score is determined by measuring in millimetres from the left hand end of the line to the point that the patient marks.

Recall Period for items

Recall period for items.Varies, but most commonly respondents are asked to report “current” pain intensity or pain intensity “in the last 24 hours.”

Scoring and Interpretation

Using a ruler, the score is determined by mea-suring the distance (mm) on the 10-cm line between the “no pain” anchor and the patient’s mark, providing a range of scores from 0–100. A higher score indicates greater
pain intensity. Based on the distribution of pain VAS scores in post- surgical patients (knee replacement, hyster-ectomy, or laparoscopic myomectomy) who described their postoperative pain intensity as none, mild, moderate, or severe, the following cut points on the pain VAS have been recommended: no pain (0–4 mm), mild pain(5-44 mm), moderate pain (45–74 mm), and severe pain (75–
100 mm) (11). Normative values are not available. The scale has to be shown to the patient otherwise it is an auditory scale not a visual one.

Merits and Demerits

The VAS is widely used due to its simplicity and adaptability to a broad range of populations and set-tings.

• VAS is more sensitive to small changes than are simple descriptive ordinal scales in which symptoms are rated,for example, as mild or slight,moderate,or severe to agonizing.
• These scales are of most value when looking at change within individuals
• The VAS takes�1 minute to complete
• No training is required other than the ability to use a ruler to measure distance to determine a score
• Minimal translation difficul-ties have led to an unknown number of cross-cultural adaptations
  
  • However, assessment is clearly highly subjective
• Are of less value for comparing across a group of individuals at one time point.
• It could be argued that a VAS is trying to produce interval/ratio data out of subjective values that are at best ordinal.
• The VAS is administered as a paper and pencil measure. As a result, it cannot be admin-istered verbally or by phone.
• Caution is required when photo-copying the scale as this may change the length of the 10-cm line and also, the same alignment of scale should be used consistently within the same
  patient

Thus, some caution is required in handling such data. 

Obtaining the scale

The pain VAS is available in the public domain at no cost. Graphic formats for the VAS may be obtained from Scott & Huskisson or online: http:// www.amda.com/tools/library/whitepapers/hospiceinltc/ appendix-a.pdf. 

Psychometric Information

Method of development.

The pain VAS originated from continuous visual analog scales developed in the field of psychology to measure well-being. Woodforde and Merskey first reported use of the VAS pain scale with the descriptor extremes “no pain at all” and “my pain is as
bad as it could possibly be” in patients with a variety of conditions. Subsequently, others reported use of the scale to measure pain in rheumatology patients receiving pharmacologic pain therapy. While variable anchor pain descriptors have been used, there does not appear to be any rationale for selecting one set of descriptors over an-other.

Acceptability

The pain VAS requires little training to administer and score and has been found to be acceptable to patients. However, older patients with cognitive impairment may have difficulty understanding and there-fore completing the scale. Supervision during completion may minimize these errors.

Reliability

Test–retest reliability has been shown to be good, but higher among literate (r�0.94,P�0.001) than illiterate patients (r �0.71,P�0.001) before and after attending a rheumatology outpatient clinic.

Validity.

In the absence of a gold standard for pain, criterion validity cannot be evaluated. For construct valid-ity, in patients with a variety of rheumatic diseases, the pain VAS has been shown to be highly correlated with a 5-point verbal descriptive scale (“nil,” “mild,” “moder-ate,” “severe,” and “very severe”) and a numeric rating scale (with response options from “no pain” to “unbear-able pain”), with correlations ranging from 0.71–0.78 and 0.62–0.91, respectively). The correlation between ver-tical and horizontal orientations of the VAS is 0.99.

Ability to detect change

In patients with chronic in-flammatory or degenerative joint pain, the pain VAS has demonstrated sensitivity to changes in pain assessed hourly for a maximum of 4 hours and weekly for up to 4
weeks following analgesic therapy (P�0.001). In patients with rheumatoid arthritis, the minimal clinically significant change has been estimated as 1.1 points on an 11-point scale (or 11 points on a 100-point scale). A minimum clinically important difference of 1.37 cm has been determined for a 10-cm pain VAS in patients with rotator cuff disease evaluated after 6 weeks of nonoperative treatment