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case control studies

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Case control study:

  • is a retrospective comparison between representative samples of people who get a disease and people who do not
  • is a type of observational study in which characteristics of subjects with a disease are compared with a selected group of control subjects without the disease. The validity of this type of study depends on the appropriate selection of control subjects. Can show associations, but cannot establish causality
  • the objective of a case control study is to validate an aetiological hypothesis or to suggest mechanisms of causation for a disease. In a case control study the comparison between groups is with respect to EXPOSURE whereas a cohort study is compared with respect to DISEASE e.g.

Case-control Study:

Establish proportion with past exposure to HRT <--------- cases of DVT/PE past exposure in menopausal women

Establish proportion with no past exposure <--------- cases of DVT/PE in menopausal women

Cohort study

HRT users -----------> incidence of breast cancer

non-HRT users -----------> incidence of breast cancer


  1. MeReC Briefing (2005);30 (supplement):1-7.