Objective: The goal of this study was to determine the minimal change in pain score recognized by patients as meaningful known as minimal clinically important difference (MCID).
Methods: Pain was recordedupon admission, 30 and 60 min later and patients were asked todescribe the extent of pain change on a 5-point Likert scale ranging from "much better" to "much worse". Patients reported their pain by two common pain scales comprising numeric rating scale (NRS) and visual analog scale (VAS). We used receiver operating characteristiccurve to assess the accuracy of pain scales. We then calculated the mean change in pain scores among patients who reported their pain change as "a little better" or "a little worse" and also analyzed regression to evaluate the MCID.
Results: A total of 150 patients and 253 pain changes were recruited. The MCID ± SD (95% CI) was 1.65 ± 1.58 (1.32-1.97) for NRS and 16.55 ± 17.53 (12.96-20.15) for VAS. The area under the curve by NRS and VAS were 0.86 and 0.89. For linear regression, the line slope and the y-intercept were 17.56 and 1.88, for VAS; these values were 1.73 and 0.31 for NRS, respectively.
Conclusions: Recognizing the extent of change in pain score that really matters to patients is crucial for the evaluation of treatment effect. Patients perceived a change of 1.65 points on NRS and 16.55 on VAS in their pain severity as meaningful. This value was not different whether the pain was perceived alleviated or aggravated.
Keywords: Minimal clinically important difference; Numeric rating scale; Pain measurement; Visual analog scale.
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