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. For example, the amount of pain that a patient feels ranges across a continuum from no pain to extreme pain.
Operationally, a VAS is usually a horizontal line, 100 mm in length, anchored by word descriptors at each end. The patient marks on the line the point that 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.
VAS are appropriate for the measurement of feelings (states of the self, moods and sensations).
There are many other ways in which VAS have been presented, including vertical lines and lines with extra descriptors.