Epidemiology is the study of factors determining and influencing the frequency and distribution of disease, injury, and other health related events and their causes in a defined human population. Epidemiology Branch investigators study a wide range of health effects linked to environmental exposures. Endpoints range from birth defects to chronic diseases, often with a focus on specific environmental contaminants. Studies typically include the collection of biological and environmental samples for assay of biomarkers of exposure or genes that affect susceptibility. The Epidemiology Branch portfolio includes multipurpose cohort studies, as well as focused studies of reproductive and women's health, children's environmental health, and cancer and chronic disease. Its mission is "to apply and extend the tools of epidemiology to study effects of the environment on human health."