ABSTRACT
Epidemiology is the study of the distribu tions and determinants of health effects and injuries in human populations. This chap ter discusses the epidemiologist’s approach and tools used in studying suspected bene ficial and adverse health effects. The areas discussed include measurement of event rates, measurement of the association be tween an exposure and an event, sources of error, study design, assessment of exposure and other factors, interpretation of results, and screening for disease. The terminology used is defined. The discussions assume that the time periods are defined over which an exposure and an event occur.
