The Minimal Clinically Important Difference Changes Greatly Based on the Different Calculation Methods.

Background: The minimal clinically important difference (MCID) for patient-reported outcome measures (PROMs) expresses both the extent of the improvement and the value that patients place on it. MCID use is becoming increasingly widespread to understand the clinical efficacy of a given treatment, define guidelines for clinical practice, and properly interpret trial results. However, there is still large heterogeneity in the different calculation methods.

Purpose: To calculate and compare the MCID threshold values of a PROM by applying various methods and analyzing their effect on the study results interpretation.

Study Design: Cohort study (Diagnosis); Level of evidence, 3.

Methods: The data set used to investigate the different MCID calculation approaches was based on a database of 312 patients affected by knee osteoarthritis and treated with intra-articular platelet-rich plasma. MCID values were calculated on the International Knee Documentation Committee (IKDC) subjective score at 6 months using 2 approaches: 9 methodologies referred to an anchor-based approach and 8 methodologies to a distribution-based approach. The obtained threshold values were applied to the same series of patients to understand the effect of using different MCID methods in evaluating patient response to treatment.

Results: The different methods employed led to MCID values ranging from 1.8 to 25.9 points. The anchor-based methods ranged from 6.3 to 25.9, while the distribution-based ones were from 1.8 to 13.8 points, showing a 4.1× variation of the MCID values within the anchor-based methods and a 7.6× variation within the distribution-based methods. The percentage of patients who reached the MCID for the IKDC subjective score changed based on the specific calculation method used. Among the anchor-based methods, this value varied from 24.0% to 66.0%, while among the distribution-based methods, the percentage of patients reaching the MCID varied from 44.6% to 75.9%.

Conclusion: This study proved that different MCID calculation methods lead to highly heterogeneous values, which significantly affect 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 MCID, as currently available, in the clinical research.