Epidemiology is the study of the different factors occurring along with diseases: their frequency, mode of transmission, evolution and implementation of necessary means for their prevention.

There is both descriptive and analytical epidemiology.

Descriptive epidemiology deals with the frequency and the distribution of risk factors in populations and enables to assess the extent of a disease. It can thus provide hypotheses of etiologic research.

Analytical epidemiology aims to research and study risk and protector factors of diseases.

Large epidemiological studies are transversal studies, case-control studies, cohort studies.