The Visual Analogue Scale (VAS) is a psychometric instrument used in research and clinical studies to measure the intensity of subjective experiences that cannot be objectively quantified using defined biomarkers, such as pain, fatigue, or mood. It typically consists of a 100 mm straight line with descriptive anchors at each end representing the extremes of the sensation (for example, “no pain” at one end and “the most severe pain imaginable” at the other). Respondents indicate their experience by marking a point on the line, and the distance from the lower anchor is measured and recorded as a continuous variable. VAS data can be analyzed using descriptive or inferential statistics, with the ordinal and non-linear properties of the scale requiring careful justification of the statistical methods applied.