Epidemiology is the study of disease behavior, particularly at the population level. Epidemiology includes study of both chronic and acute conditions and of both infectious and non-infectious diseases. It can also refer to social phenomena, such as gun violence or certain behaviors.
Deeper dive
This science encompasses the incidence and prevalence of a disease or conditions, disease risk factors, surveillance strategies and efforts, biostatistics, prevention strategies, treatment strategies, transmission modalities and risks (particularly for infectious diseases), etiology of the condition, patterns in disease behavior, the natural history of a disease, and any other information necessary to understand disease behavior and to prevent, stop, or treat disease.
Observational studies—which comprise the vast majority of studies that are not randomized controlled trials—are also commonly called epidemiological studies because they nearly always involve observing a large population and drawing inferences from those observations. In circumstances where randomized controlled trials cannot answer a particular question, whether for ethical or logistical reasons, epidemiological research may be able to if enough data exist from enough well-designed studies. (See Hill criteria for more on how epidemiological/observational studies can contribute to conclusions about causation.)