Analytic epidemiological studies
Analytic epidemiological studies aim to investigate and identify factors associated with the presence of disease within populations. These factors can be classified as one of the components of the 'epidemiological triad' of:
Host
Agent
Environment
Host factors
These include unchanging characteristics of the host animal such as sex, breed or species, as well as more variable characteristics such as age, nutritional status and stage of pregnancy.
Agent factors
Features of the agent which affect the levels of disease within an infected population
Environment factors
Analytic studies
Analytic studies may investigate exposure to these factors in animals with disease, compared to those without, or may compare the occurrence of disease amongst 'exposed' animals to 'unexposed' animals. Although there are considerable difficulties in establishing causation of disease, the results of these studies can provide useful evidence regarding possible risk factors.