Challenges in applying minimal clinically important difference: a critical review

Healthcare clinicians strive to make meaningful changes in patient function and participation. A minimal clinically important difference (MCID) is an estimate of the magnitude of change needed to be meaningful to a patient. Clinicians and investigators may assume that a cited MCID is a valid and generalizable estimate of effect. There are, however, at least two concerns about this assumption. First, multiple methods exist for calculating an MCID that can yield divergent values and raise doubt as to which one to apply. Second, MCID values may be erroneously generalized to patients with dissimilar health conditions. With this in mind, we reviewed the methods used to calculate MCID and citations of reported MCID values for outcome measures commonly used in neurologic, orthopedic, and geriatric populations. Our goal was to assess whether the calculation methods were acknowledged in the cited work and whether the enrolled patients were similar to the sample from which the MCID estimate was derived. We found a concerning variation in the methods employed to estimate MCID. We also found a lack of transparency in identifying calculation methods and applicable health conditions in the cited work. Thus, clinicians and researchers must pay close attention and exercise caution in assuming changes in patient status that exceed a specific MCID reflect meaningful improvements in health status. A common standard for the calculation and reporting of an MCID is needed to address threats to the validity of conclusions drawn from the interpretation of an MCID.