15. Causation in epidemiology: association and causation

From greek.doctor
  • Causation: whether an exposure actually causes a specific disease
    • or: whether the association between an exposure and a disease is causative
    • Bias, confounding and chance must all be eliminated to establish a causal relationship
  • Koch’s postulates for causation (of infectious diseases) states that the causative agents can:
    • Be isolated from the affected organism in a culture
    • Be cultured
    • Produce the same disease in a second animal
    • Be isolated from the second animal
  • Epidemiological triangle
    • Host factors, environmental factors and the causative agent all play a role in disease development
  • Causative agents can be nutrients, poisons, microorganisms, radiation, trauma, etc.
  • Host factors can be genetic susceptibility, immunological state, age, lifestyle, etc.
  • Environmental factors can be crowding, housing, atmosphere, etc.
  • Five rules (of causation) in epidemiology (similar to the Bradford-Hill criteria)
    • There must be a high relative risk
    • The results must be consistent
    • There must be a graded response to a graded dose
      • I.e., a higher dose increases risk
    • There must be a temporal relationship, i.e. the disease must occur after the exposure
    • There must be a plausible mechanism by which the exposure causes the disease
  • The British Doctors’ study was historical, as it proved the causation between smoking and lung cancer