Minimal clinically important difference, low disease activity state, and patient acceptable symptom state: methodological issues.

The importance of determining a minimal clinically important difference (MCID) and a low disease activity state (LDAS) as treatment targets in clinical trials no longer needs to be demonstrated. However, many methodological issues remain: whether these thresholds should be defined for each criterion or for composite criteria, whether there is a difference between the LDAS and patient acceptable symptom state (PASS), how to determine these thresholds (i.e., the wording of the questions and the statistical approach), and whether there are confounding factors in their evaluation. We consider these methodological issues and discuss their impact. Methods to determine the thresholds must be standardized, and recommendations could be endorsed by an OMERACT module. Threshold values for the MCID and LDAS should be determined according to data-driven and experts' opinions and approaches.