Abstract
Epidemiology can be applied to any field which produces adverse effects upon the individual. It should, therefore, have three main aims: (1) To describe the distribution and extent of a participation problem; (2) To provide data essential to the planning, implementation and evaluation of the services to be ultimately developed to prevent, control and deal with the consequences of the given situation; and (3) To identify the etiological factors present in the development, or natural history, of a particular problem.