The visual analogue scale: its use in pain measurement.

Use of pain rating scales, especially the visual analogue scale (VAS), has increased dramatically in the last decade. Consideration of the VAS in terms of its physical structure and the patient's behaviour when confronted with the scale, casts doubt on its validity. It is non-linear and prone to bias which limits its use as a serial measure of pain severity. Measuring pain intensity alone imposes further limitations. The McGill Pain Questionnaire measuring several dimensions of pain appears to be a better alternative.