ABSTRACT
For prevention and management of asthma, information is needed on patterns of disease occurrence, risk factors, and natural history, including the impact of therapy on disease outcome. Much of this information is obtained through epidemiologic investigation. Epidemiology is defined as the scientific methods used to study disease occurrence in human populations. Although formal definition of this discipline has been difficult, the emphasis on human populations differentiates epidemiology from conventional clinical research that addresses patient groups. Epidemiology may be considered to have two distinct components: description of disease occurrence, most often by person, place, or time; and the identification of risk factors for disease.1 Experimental study designs, such as the controlled clinical trial, are also used to evaluate therapeutic modalities and to conduct health services research.
