Minimum clinically important difference: the crock of gold at the end of the rainbow?

The minimum clinically important difference (MCID), like the crock of gold at the end of the rainbow, is attractive but unattainable. Empirical data on how rheumatologists make clinical decisions show a wide variety of approaches and lack of agreement in decision making. Clinical importance needs to consider the magnitude of both the benefits and adverse events. A proposal for future attempts to define MCID could explore links between short term changes in outcomes to improvement in disability outcome many years later. Defining response to treatment could be explored using different approaches and involving patients and other professional groups.