The Minimal Clinically Important Difference: Response

We thank Matthew S. Tenan and Christopher Boyer for their letter to the editor and the interest and appreciation shown in our work, which provided important insights on the complexity of the minimal clinically important difference (MCID), a parameter increasingly used to evaluate the results of clinical trials and determine the clinical relevance of a specific treatment.2 This study showed that different methods used to calculate MCID lead to highly heterogeneous values, which significantly affects the percentage of patients achieving the MCID in a given population. The wide-ranging thresholds obtained with the different methodologies make it difficult to evaluate the real effectiveness of a given treatment, questioning the usefulness of the MCID, as currently available, in the clinical research.1 Like the authors of the letter, we disagree with the current mindset that identifies the MCID as a threshold to be crossed, which can be obtained using an arbitrarily chosen method. Conversely, they advocated a 3-pronged approach to identify the MCID, as recommended by the Food and Drug Administration, to reach more meaningful results.3 We also agree that MCIDs should be used as ranges or thoughtful rules of thumb and not thresholds to be crossed. Even more, we feel the most critical point remains the desire for a “simple” threshold, which is the way the MCID is used clinically and often prescribed in the research literature. Considering the limitations of the MCID, caution is needed when reporting and interpreting the MCID of a given patient-reported outcome measure as a measure of a treatment effectiveness both in the clinical setting and in research.4 Failure to acknowledge these limitations runs the risk of misclassifying patients below a preselected MCID as nonresponders when in fact they have improved. On the flip side, there is also risk of overestimating the number of responders in patient groups with more acute symptoms or disease severity.5 Until more clarity is reached in this field, the comparison of the percentage of patients reaching the MCID among different studies should be performed only when the same methodology is applied, and given the inherent limitations in the current MCID score methodologies and applications, MCID should not be considered a main study outcome but rather one of the outcome measures within a more complete assessment to document treatment results. Clarity is needed and guidelines are necessary to converge on a common language to assess the results in our patients and provide a more consistent body of knowledge on the minimal benefits provided by the different treatments that are perceived as clinically important.