Epidemiology is the study of disease occurrence and health indicators in human populations. The focus on populations distinguishes Epi from other biological sciences and medicine; the focus on disease and health distinguishes it from the social sciences. As an applied scientific discipline in public health, Epi involves the integration of theory, knowledge, and skills from the biomedical sciences, the social sciences, and mathematical disciplines such as statistics.
The aims of epidemiologic research are broad, and include description, explanation, prediction, and control of the occurrence of disease and health problems in target populations. Although epidemiologic methods and reasoning are used in all fields of public health and medicine, epidemiologists themselves devote considerable attention to identifying biological, behavioral, psychosocial, occupational, and environmental factors that influence the natural history of disease and to estimating these effects. In addition, epidemiologists are involved in detection, investigation, and control of local disease outbreaks and clusters; the assessment of health-care needs in populations and health services; the evaluation of public-health and medical interventions; the surveillance of specific populations for new cases of disease and injuries; the study of health-related behaviors; risk assessment and policy development; and the development of new research methods.