Problems associated with pain measurement in arthritis: comparison of the visual analogue and verbal rating scales.

Thirty-seven arthritis patients participating in a drug withdrawal trial, simultaneously completed a 20-point visual analogue scale and 7-point verbal rating scale for pain severity while on active medication and 48 hours following its withdrawal. The relationship between the two scales could be better approximated by a curve than a straight line, and further interpretation suggested that the relationship might be sigmoidal. This indicates that only the middle of the scales are linearly related with a lack of agreement occurring towards the upper and lower ends. Although the visual analogue scale proved superior to the verbal rating scale in its ability to detect changes in pain, until more is known about factors which influence subjective magnitude estimation, this conclusion must remain tentative. The implications of the findings to pain measurement are discussed.