The Minimum Clinically Important Difference in Physician–assigned Visual Analog Pain Scores

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Abstract
To determine the minimum clinically important difference in physician-assigned visual analog scale (VAS) pain scores. Physicians attending emergency medicine didactic conferences were enrolled in this descriptive study. The subjects sequentially reviewed 11 written scenarios describing patients in moderate to severe pain. The subjects rated their perceptions of each patient's pain on a 100-mm VAS, then contrasted this pain with that of the previous patient scenario. For these contrasts, the subjects chose one of five responses: "much less," "a little less," "about the same," "a little more," or "much more" pain. The minimum clinically important difference was defined as the difference between scores for scenario pairs in which one patient's pain was rated "a little less" or "a little more" severe. There were 230 comparisons by 23 health professionals. Of these, 64 were judged "a little less," and 56 "a little more," painful. These 120 comparisons, with their pain score differences, were used to determine the minimum clinically important difference. Pain judged to be "a little less" or "a little more" severe was associated with a mean difference in VAS scores of 18 mm (95% CI 16-20 mm), corresponding to a decrement of 23% (95% CI 20-26%) from the more painful scenario. Pain research outcomes involving a < 18-mm difference, or a 23% decrement in physician-assigned VAS pain scores, although statistically significant, may have little clinical importance.