Minimal clinically important difference and Edmonton Symptom Assessment Scale

The Edmonton Symptom Assessment Scale is one of the most widely available and used patient-reported symptom assessment tools in both clinical and research practice. Given such extensive implementation, we welcome the estimate of minimal clinically important difference (MCID) provided by Hui et al for use in sample size calculations.1 The authors have used both patient-anchored and statistical methods to estimate the MCID. This should help to distinguish between minimal detectable difference and minimal clinically important difference.2, 3 The calculated sensitivity and specificity of each item of the Edmonton Symptom Assessment Scale use the patient's global impression as the patient anchor to create a binary MCID. The sensitivity analysis suggests that a moderate effect size equates to a greater than 1-point change for many symptoms, with values around 1 equating to a small effect size, but the authors have not commented on this. Their findings were compared with other work that estimated the MCID of other components of the Edmonton Symptom Assessment Scale. Our group has calculated the MCID for chronic breathlessness for a standalone 0 to 10 numerical rating scale. The MCID of a change of 1 point on the breathlessness scale found by Hui et al is remarkably similar to the findings of our secondary analysis of data from 4 clinical trials of opioids for refractory breathlessness.6 Furthermore, because the MCID in Johnson et al was assessed by patient-anchored (blinded patient preference) and statistical distribution methods, we were able to determine that such a change would be both a moderate effect size and a difference that resulted in patient-led treatment choice. Our findings from the distribution method were remarkably similar to the estimate derived from Hui et al's standard-error-of-measurement sensitivity analysis1 (an 11.3-mm moderate effect size for Johnson et al6 vs a 1.2-point change for 0.5 standard deviations for Hui et al). Although the patient population in Johnson et al's study included people with cancer and noncancer life-limiting illnesses causing breathlessness, a pooled data analysis showed that etiology was not a predictor of response to breathlessness, and this MCID for chronic refractory breathlessness was relevant regardless of the underlying etiology; this is an important finding in itself.7 The MCID is important in both clinical and research practice. Methodological work that provides a nuanced understanding is crucial because of the flow-on effects of the findings on clinical trial design and even reimbursement decisions. No specific funding was disclosed. David C. Currow reports that he is an unpaid advisory board member for Helsinn Pharmaceuticals. He has received an unrestricted research grant from Mundipharma and is a consultant to Mayne Pharma. Miriam J. Johnson reports that she is a consultant to Mayne Pharma. Miriam J. Johnson1 1Hull York Medical School University of Hull Kingston Upon Hull, United Kingdom David C. Currow2 2Discipline of Palliative and Supportive Services Flinders University Adelaide, Australia