ABSTRACT
Epidemiological studies contribute to the prevention of cancer. The hypotheses about the cause of cancer can be tested by relating the occurrence of the disease to a personal characteristic of the affected individuals—either to their constitution or to the degree to which they have been exposed to an environmental agent. Large parts of the world have only recently been opened up to medical research and there is still very little quantitative information about the incidence of any type of cancer outside Europe and North America. Evidence of an association is, therefore, indirect and though it may be extremely valuable in suggesting a hypothesis for detailed study by other methods, definite conclusions about aetiology cannot be drawn from it. Epidemiology can make an important contribution by the carefully designed collection of observations on individual subjects and a detailed statistical analysis of the results.
