A study where patients who have developed a disease are identified (cases) and past exposure to suspected aetiological factors is then compared with a group of controls who do not have the disease
Allowance for possible confounding factors can be made by appropriate adjustments in the analysis. Matching cases and controls or exposure to confounders, either on an individual basis (e.g by pairing each case with a control of the same age and sex) or in groups (for example, choosing a control group with an overall age and sex distribution similar to that of the cases) makes statistical adjustment more efficient.
- quick and cheap
- only feasible method for very rare disorders or those with long lag between exposure and outcome
- fewer subjects needed than cross-sectional studies.
- reliance on recall or records to determine exposure status
- selection of control groups is difficult
- potential bias: recall, selection.