Interpretation of visual analog scale ratings and change scores: a reanalysis of two clinical trials of postoperative pain.

The visual analog scale (VAS) is one of the most commonly used measures of pain intensity in pain research. However, there remain important unanswered questions concerning interpretation of specific VAS ratings and change scores. To address these questions, we performed a reanalysis of data from 2 randomized controlled trials of postoperative pain (N = 123 and N = 125) to determine the meaning of VAS pain intensity ratings and change scores. The findings suggested that 100-mm VAS ratings of 0 to 4 mm can be considered no pain; 5 to 44 mm, mild pain; 45 to 74 mm, moderate pain; and 75 to 100 mm, severe pain. As predicted, in assessment of the amount of change corresponding to differing levels of pain relief, percentage change in a patient's VAS score was less biased by pretreatment pain than was absolute change score. The findings also suggested that a 33% decrease in pain represents a reasonable standard for determining that a change in pain is meaningful from the patient's perspective.