Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control health problems at the group level. The major objectives of epidemiologic studies are to describe the extent of disease in the community, to identify risk factors (factors that influence a person’s risk of acquiring a disease), to determine etiology, to evaluate both existing and new preventive and therapeutic measures (including health care delivery), and to provide the foundation for developing public policy and regulatory decisions regarding public health practice.