Study objective: To determine the amount of change in pain severity, as measured by a visual analog scale, that constitutes a minimum clinically significant difference.
Methods: Patients 18 years of age or older who presented with acute pain resulting from trauma were enrolled in this prospective, descriptive study. The setting was an urban county hospital emergency department with a Level 1 trauma center. In the course of a brief interview, patients were asked to indicate their current pain severity with a single mark through a standard 100-mm visual analog scale. At intervals of 20 minutes for the next 2 hours, patients were asked to repeat this measurement and, in addition, to contrast their present pain severity with that at the time of the previous measurement. They were to indicate whether they had "much less," "a little less," "about the same," "a little more," or "much more" pain. All contrasts were made without reference to prior visual analog scale measurements. A maximum of six measurements of pain change were recorded per patient. Measurements ended when the patient left the ED or when the patient reported a pain score of zero. The minimum clinically significant change in visual analog scale pain score was defined as the mean difference between current and preceding visual analog scale scores when the subject noted a little less or a little more pain.
Results: Forty-eight subjects were enrolled, and 248 pain contrasts were recorded. Of these contrasts, 41 were rated as a little less and 39 as a little more pain. The mean difference between current and preceding visual analog scale scores in these 80 contrasts was 13 mm (95% confidence interval, 10 to 17 mm).
Conclusion: The minimum clinically significant change in patient pain severity measured with a 100-mm visual analog scale was 13 mm. Studies of pain experience that report less than a 13-mm change in pain severity, although statistically significant, may have no clinical importance.