Statistical analysis of chronic obstructive pulmonary disease exacerbations in clinical studies: expectations and limitations.

Acute exacerbations of chronic obstructive pulmonary disease (COPD) occur more frequently with increasing COPD severity and are associated with increased morbidity, reduced quality of life, and increased risk of mortality. The prevention and assessment of exacerbations, as a clinically and therapeutically relevant parameter, is a central aspect of clinical COPD studies. The aim of this review is to identify pitfalls in the analysis of the parameter of exacerbation and to describe the criteria that need to be considered in the statistical analysis of exacerbation studies.