Study objectives: The purpose of this study is to determine the minimum clinically significant difference in a patient-assigned, 11-point numeric rating scale (NRS-11) score for the assessment of pain in adult emergency department (ED) patients.

Methods: This prospective, observational study was approved by the hospital institutional review board. A tertiary care academic ED served as the study setting. ED patients presenting with pain consented and were enrolled in this study by an investigator or a trained research assistant. Patients were asked to rate their pain on the NRS-11, a scale of 0 to 10, with 0 being “no pain” and 10 being “the worst pain they could imagine” on entry into the study. Patients were asked to reevaluate their pain intensity every 20 minutes for 2 hours on the NRS-11. Patients contrasted this pain with their pain intensity at the previous evaluation. For the contrast, patients were asked to choose 1 of the following responses: “a lot more pain,” “a little more pain,” “about the same pain,” “a little less pain,” or “a lot less pain.” The minimum clinically significant difference was defined as the difference between scores when a patient's pain was rated “a little more” or “a little less” severe.

Results: Three hundred one patients were enrolled in the study, and 1,192 comparisons were made. Of these comparisons, 187 were rated as “a little less pain,” and 82 were rated as “a little more pain.” The mean difference between current and preceding NRS-11 scores in these 269 comparisons was 1.41 (SD±1.05; 95% confidence interval [CI] 1.28 to 1.54).

Conclusion: These findings suggest that the minimum clinically significant difference in patient-assigned NRS-11 pain scores is 1.41 (SD±1.05; 95% CI 1.28 to 1.54). Studies that report a change of less than 1.41 points may indicate statistical significance, but the findings may not have clinical significance. Additional research is needed to determine whether the minimum clinically significant difference varies with age, race, or ethnicity.