Translations:Advanced Field Epi:Manual 1 - Disease Investigation/309/en
Selection of animals
In a case-control study, the cases must have the disease being investigated, meaning that they must meet the case definition. The case definition must also be independent of the risk factors that are being studied. It is generally best to use the confirmed case definition and to try and restrict the selected cases to those animals that are likely to be recent cases as opposed to animals that may have been infected some time ago (chronic cases). If some of the cases die as a result of the disease then studying chronic cases may be more informative about factors that influence survival than factors that determine risk of occurrence of disease.