Case-Control Study

An observational study that compares patients who have a disease or outcome of interest (cases) with patients who do not have the disease or outcome (controls). It looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group. This allows the investigator to decide upon the relationship between the risk factor and the disease.

Case-control studies are observational because there is no intervention and no attempt is made to alter the course of the disease. The goal is to retrospectively decide upon the exposure to the risk factor of interest from each of the two groups of individuals: cases and controls. These studies are designed to estimate odds or chances.
Case-control studies are also known as ‘retrospective studies’ and ‘case-referent studies’.

Advantages Disadvantages
  • Good for studying rare conditions or diseases.
  • Less time needed to conduct the study because the condition or disease has already occurred.
  • Lets you look at multiple risk factors at the same time.
  • Useful as initial studies to establish an association.
  • Can answer questions that could not be answered through other study designs.
  • Retrospective studies have more problems with data quality because they rely on memory. People with a condition will be more motivated to recall risk factors (also called ‘recall bias’).

  • Not good for evaluating diagnostic tests because there is not a control group (all cases have the condition).

  • It can be difficult to find a suitable control group.