Study design

Epidemiological studies fall into one of two categories: descriptive or analytical. Descriptive studies involve detailed investigations of individuals in order to improve knowledge of disease. Descriptive studies often have no prior hypotheses and are opportunistic studies of disease whereas analytical studies are used to test hypotheses by selection and comparison of groups. However, data obtained from analytical studies can be used in a descriptive manner and vice versa.

Descriptive studies

Descriptive studies include case-series and case-reports, involving rigorous descriptions of disease from the study of individuals. Although unable to test hypotheses, as they do not involve the comparison of groups, they improve knowledge and understanding of disease and are useful for generating hypotheses.

Analytic studies

Analytical studies are used to test hypotheses by comparison of groups of animals based on their exposure or disease status. Analytical studies can be observational or experimental, in observational studies the experimenter does not apply an intervention to the animals or manipulate their environment they simply observe or take measurements.