Summary by Chapters

Abstract

Epidemiology is concerned with the occurrence, cause, and course of disease within populations, and the discovery of factors which tend to precipitate or prevent its appearance. Basic to this study is the definition of the disease, which is a necessary prerequisite to the determination of its frequency. The principal methods to ascertain the latter are the calculation of prevalence and incidence rates, and, for some disorders, mortality rates. The prevalence (rate) of a disease is the number of cases per unit population present at one time, and the incidence and mortality rates refer to the number of new cases or the number of deaths per unit population taking place in a given period, usually one year.