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Association to Causation

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Association to Causation

  1. 1. Association to Causation BY DR MUHAMMAD TAUSEEF JAVED CONSULTANT MINISTRY OF HEALTH MAKKAH & IPH LAHORE
  2. 2. Sequence of Studies Clinical observations Available data Case-control studies Cohort studies Randomized trials
  3. 3. Types of Associations • Real • Spurious
  4. 4. DEFINITIONS • Observational study • Causation • Etiology • Association • Necessary • Sufficient Your Assignment: Define these terms as they apply to epidemiology.
  5. 5. Koch and Causation • Postulates • Why study association? • Web of causation • Do we need a better way?
  6. 6. Twelve Criteria for Causation • Cause distributed at same level • Incidence much higher in exposed population • Exposure more frequent • Disease should follow exposure • Dose dependent • Expected response • Association should be the same • Other cause-effect ruled out • Control results in decreased disease • Modification of host results in decrease • Human vol. always + • Findings should make sense
  7. 7. Factors in Causation of Disease • Predisposing • Enabling • Precipitating • Reinforcing Your Assignment: Define these terms as they apply to epidemiology.
  8. 8. Web of Causation
  9. 9. Are Associations Always Connected to the Disease? NO, BUT ………………………….. Cigarette smoking and lung cancer Age and prostate cancer Car accidents and alcohol Tribal customs and kuru Agriculture and antibiotic resistance
  10. 10. Association • Deals with ………………. • Is concerned with ………. • Is the degree of …………. • Has to be scientifically proven ….. Your Assignment: fill in the blanks
  11. 11. Degrees of Association • No association Direct association No possibility for association Possibly associated Associated Direct cause and effect
  12. 12. Guidelines for Judging Whether An Association Is Causal • Temporal relationship • Strength of the association • Dose-response relationship • Replication of the findings • Biologic plausibility • Consideration of alternate explanations • Specificity of the association • Consistency with other knowledge
  13. 13. Deriving Causal Inferences • Arriving at causation from association  For example, showing that Helicobacter pylori is directly linked to peptic ulcers
  14. 14. Perspectives • Causation may be limited • Subject to modification • Perhaps more complex than realized • Sometimes not measureable • “Criteria” are really guidelines may be subjective

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