The principle of Epidemiology is the increased understanding of all aspects of any health-related event with an ultimate goal to improve the quality of life. Epidemiology has succeeded in realizing that for any health-related event there are modifiable risk factors and/or causes. The challenge in epidemiology was to promote the role of prevention in medicine in two main directions. First, early detection and treatment of diseases to help in reducing the clinical manifestations and mortality among diseased individuals. Second, early detection and intervention for risk factors to help in reducing disease incidence among healthy individuals. Screening was the tool used by epidemiologists in this respect.