22. Case-control studies

From greek.doctor
  • Most frequently performed epidemiology studies
  • A retrospective study – healthy and sick people are found, and their previous exposure to a factor is determined
  • Aim: to study if an exposure (usually a risk factor) is associated with a disease
  • Steps
    • Select patients with the disease = the cases
    • Select persons without the disease with similar baseline characteristics as the cases = the controls
    • Compare the exposure of risk factors between these groups
      • Find how many of the cases were exposed to the risk factor
      • Find how many of the cases were not exposed to the risk factor
      • Find how many of the controls were exposed to the risk factor
      • Find how many of the controls were not exposed to the risk factor
    • The odds ratio between the groups is determined
  • Controls
    • Should be picked from the same source population as the cases
    • Must be at risk of the disease
    • Must have comparable characteristics as the cases
  • Pros
    • Fast, cheap
    • Good for rare diseases
    • Can study multiple exposures
  • Cons
    • Can’t determine incidence rate
    • Does not provide relative risk (RR)
    • Possibility of recall and selection bias
  • Example
    • Richard Doll’s study which established the link between smoking and lung cancer