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Association Causation

Association Causation. Marshall Tulloch-Reid Epidemiology Research Unit Tropical Medicine Research Institute. Objectives. Differentiate Association from Causation Understand the causal pie model for disease causation

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Association Causation

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  1. AssociationCausation Marshall Tulloch-Reid Epidemiology Research Unit Tropical Medicine Research Institute

  2. Objectives • Differentiate Association from Causation • Understand the causal pie model for disease causation • List and discuss some of the criteria that have been used for deciding between association and causation – Henle Koch Postulates & the Bradford Hill Criteria • Understand the limitations of these criteria

  3. Association Causation • Variables are associated if a statistical relationship exists between them • Statistical association does not imply a causal relationship between the variables

  4. Association Causation

  5. Association Causation r = 0.5

  6. Association CausationHats and Obesity Percent Hats Percent Obese Group A B C 20 40 60 20 40 60

  7. Concepts in Causation • The trigger of an event is often thought of as its cause • Most events are the result of the interaction of several causes • These causes do not need to occur simultaneously

  8. Concepts in Causation A 88 year old women with uncontrolled type 2 diabetes and poor vision from diabetic retinopathy and glaucoma falls and fractures her hip. What caused the hip fracture?

  9. The fall Poor vision Hypoglycemia Neuropathy Non-compliance with treatment Age Osteoporosis Genetic factors No non-skid rug Not wearing a hip protective device The dog Concepts in CausationWhat caused the hip fracture?

  10. E D A C B The Causal Pie Single Component Cause Sufficient Cause

  11. The Causal Pie SF II SF I SF – sufficient cause SF III

  12. The Causal Pie • Sufficient cause • Component Cause • Necessary Cause

  13. Causality and the Scientific Method Inductive method • Observations induce in the mind of the observer a suggestion for a more general statement • David Hume – inductive method depends on circular reasoning

  14. Causality and the Scientific Method Refutation Karl Popper – statements about nature canbe corroborated by evidence but it does not amount to logical proof; however statements can be refuted by deductive logic

  15. Criteria for Causation • A checklist is often employed to resolve issues of causation vs. association • Koch and Henle proposed criteria for infectious agents causing disease • The Bradford-Hill criteria is most often used for this purpose and can be more generally applied

  16. Criteria for Causation First questions to be answered • Are the findings due to chance? • Are the findings due to bias? • Are the findings due to confounding?

  17. Criteria for CausationHenle-Koch Postulates • The organism is always found with the disease • The organism is not found in any other disease • The organism, isolated from one who has the disease, and cultured through several generations, produces the disease (in experimental animals)

  18. Temporal relationship Strength of the association Dose-response relationship Replication of findings Biologic plausibility Alternative explanations Cessation of exposure Specificity of the association Consistency with other knowledge Criteria for CausationBradford Hill Criteria

  19. Criteria for Causation • Not all the criteria have to be meet for causality to be implied • Some criteria carry more weight than others

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