Epidemiology is the study and analysis of the distribution, patterns, and determinants of health and disease conditions in a defined population. It is a cornerstone of public health and shapes policy decisions and evidence-based practice. Epidemiology has helped develop methodology used in clinical research, public health studies, and basic research in the biological sciences. Major areas of epidemiological study include disease causation, transmission, outbreak investigation, disease surveillance, environmental epidemiology, forensic epidemiology, occupational epidemiology, screening, biomonitoring, and comparisons of treatment effects such as in clinical trials.

Epidemiology is concerned with the incidence of disease in populations and does not address the question of the cause of an individuals disease. Epidemiological information is used to plan and evaluate public health programs and to identify risk factors for diseases. Epidemiologists collect data on the number of people affected by a disorder or disease, how many people have a disease or disorder, if those numbers are changing, and how the disorder affects society and the economy. Key terms to know in this field include incidence, prevalence, and burden of disease.

Epidemiology is the foundation of public health and is defined as the study of the “distribution and determinants” of diseases or disorders within groups of people, and the development of knowledge on how to prevent and control them. Epidemiological research helps us understand not only who has a disorder or disease but why and how it was brought to this individual or region. Epidemiology can cover a wide range of issues, from unintentional injuries to psychosocial stress.

The field of epidemiology deals with the study of distributions, causes, prevention, and the control of acute and chronic diseases in populations. Epidemiologists seek to learn why, how, and when some people contract diseases when others do not. The answers to these questions are necessary for monitoring the health status of a population, for developing new medical treatments and disease prevention efforts, and for providing an evidence base to health care and policy leaders. For these reasons, epidemiology is considered a cornerstone of public health practice.