Recommendations for epidemiological studies on COPD.

The prevalence of chronic obstructive pulmonary disease (COPD) has been extensively studied, especially in Western Europe and North America. Few of these data are directly comparable because of differences between the surveys regarding composition of study populations, diagnostic criteria of the disease and definitions of the risk factors. Few community studies have examined phenotypes of COPD and included other ways of characterising the disease beyond that of spirometry. The objective of the present Task Force report is to present recommendations for the performance of general population studies in COPD in order to facilitate comparable and valid estimates on COPD prevalence by various risk factors. Diagnostic criteria in epidemiological settings, and standardised methods to examine the disease and its potential risk factors are discussed. The paper also offers practical advice for planning and performing an epidemiological study on COPD. The main message of the paper is that thorough planning is worth half the study. It is crucial to stick to standardised methods and good quality control during sampling. We recommend collecting biological markers, depending on the specific objectives of the study. Finally, studies of COPD in the population at large should assess various phenotypes of the disease.