ABSTRACT
Epidemiology is defined as the study of the distribution and determinants of health-related states and events, and the application of this study to control of health problems (Last 1995). Descriptive epidemiology provides valuable data for the administration and health care providers to plan and implement health policy and to evaluate its effectiveness. Etiologic epidemiology aims at identifying the risk factors of diseases and provides the basis for the action to prevent the diseases by reducing or eliminating exposure to the risk factors. The third type is prognostic (or intervention or experimental) epidemiology in which the effectiveness of interventions (change of exposure, interventions to alter the course of a disease) is studied.
