How can we assess outcomes of clinical trials: the MCID approach.

Interpreting changes in outcomes of clinical trials in chronic obstructive pulmonary disease should be viewed from a broader perspective than only the statistical significance of the findings. The minimal clinical difference in outcome measures provides a conceptual framework to assist in clinical trial interpretation and a methodology to assess the clinical relevance of study results. Use of distribution-based techniques, comparison with other external measures, and opinions from experts, clinicians and patients can assist in minimal clinically important difference development. Although the minimal clinically important difference has been suggested for a wide range of outcomes of importance in chronic obstructive pulmonary disease, many have not been subjected to rigorous analysis. For newer tools such as activity monitors and questionnaires and measures not widely employed such as laboratory-based exercise tests, minimal clinically important differences remain to be determined.