The contribution to understanding the pathogenesis of cancer by current epidemiologic studies is well illustrated by the evolving literature in alimentary tract tumors. Epidemiologic techniques study the distribution of cancer and seek to uncover its determining factors; they are concerned with the search for clues of excessive prevalence of a disease. The application of epidemiologic methods to noninfectious diseases like cancer has provided a new system of investigation for uncovering the relationship of human cancer to man's environment. The ultimate goal is to understand the causal mechanisms that form a basis for preventive measures.
In order to establish a causal association between diseases and environmental exposure, a rate of occurrence or disease frequency (tumor incidence) must be determined. "Incidence" has acquired a precise meaning in epidemiologic usage during the past decade; it means the number of new cases observed in a certain time period and in a specified population of