Case-control studies

This study begins with cases (diseased subjects) and the controls (non-diseased subjects) and then investigates their exposure status.

Case-control studies are performed when the population at risk is not known or it is impractical to follow up the whole population at risk. Remember that controls should have the same chance of being exposed to the risk factors as the cases.

These studies are quick and often the first line of enquiry into any rare disease or newly emerging disease of uncertain aetiology. For example Human BSE, Legionnaire's disease, AIDS, Severe acute respiratory disease (SARS). All of these conditions were initially investigated using case-control studies.