ABSTRACT
Epidemiology is the study of disease frequency in human populations. Examples o f populations of interest to epidemiologists include the residents o f a city, the employees o f a hospital, or groups of patients with specific diseases. Epidemiologic methods are useful to address a broad range of questions concerning such popula tions, including the determination of the prevalence and incidence o f disease, the identification of risk factors, the assessment of prognosis in sick subjects, and the determination of the effectiveness of treatments. This Chapter considers applica tions of epidemiology to surgical practice and research.
