Causation Analysis in Occupational and Environmental Medicine

1. Causation Analysis in Occupational and Environmental Medicine “Establishing causation means identifying the most probable cause of a worker’s condition or disability, and also demonstrating that it arose out of the work or workplace.” Tee L. Guidotti and Susan Rose, Science on The Witness Stand, OEM Press, 2001.

2. Medical v. Legal Causation Causation in Medicine Requires an Analysis Causation in Law Requires a Determination “There are important differences between the quest for truth in the courtroom and the quest for truth in the laboratory. Scientific conclusions are subject to perpetual revision. Law, on the other hand, must resolve disputes finally and quickly.” Supreme Court’s 1993 Daubert v. Merrill Dow Pharmaceuticals, Inc.

3. “In the scientific arena, no causal hypothesis can be proven absolutely, no matter how much evidence exists in its favor” (MargaretA Berger, The Supreme Court’s Trilogy on the Admissibility of Expert Testimony, Reference Manual on Scientific Evidence, Second Edition.)Law looks to science to prove something; Scientists respond by stating that nothing is, in fact, absolutely provable.

4. Daubert, Supreme Court • Key Question: Whether a Scientific Theory can and has been Tested. “Scientific methodology today is based on generating hypothesis and testing them to see if they can be falsified; indeed, this methodology is what distinguishes science from other fields of human inquiry” • Status of Scientific Theory is based upon its Testability • Whether the Theory has been subjected to Peer Review and has been Published

5. Daubert Decision: Courts should consider admissibility of scientific theory based, non-exclusively, on: Testability Peer Review and Publication Potential Rate of Error Standards for Controlling Operation

6. Federal Rules of Evidence Amended Rule 702 , effective Dec. 2000 If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expertby knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if: • The testimony is based upon sufficient facts or data. • The testimony is the product of reliable principles and methods, and • The witness has applied the principles and methods reliably to the facts of the case.

7. Medical Causation Scientific Proof

8. How do Scientists “Prove” a Cause and Effect Relationship? Epidemiology = The Study of Epidemics (Disease in Human Populations) An epidemiological study seeks to establish that a relationship exists between agent A (cause) and disease D (effect) Does Exposure to Agent A Cause Disease D?

9. Association v. Causation Association: Statistical Relationship between two or more Variables or Events. Events are Associated when they occur More or Less Frequently than would be expected by Chance. The presence of an Association Does Not Imply that an observed relationship is one of Cause and Effect.

10. Association isNOT Equivalent to Causation Smoking Associated with Lower Socioeconomic Class However, Smoking Does Not Cause Lower Socioeconomic Class

11. Bradford Hill Criteria • None of these nine viewpoints can bring indisputable evidence for or against a cause and effect hypothesis---what they can do, with greater or lesser strength, is to help answer the fundamental question– Is there any other way of explaining the set of facts before us, is there any other answer equally, or more, likely than cause and effect?” Doll, R. (1991). Sir Austin Bradford Hill and the progress of medical science. British Medical Journal, 305, 1521-1526.

12. Bradford Hill Criteria • 1: Strength of Association: The stronger the relationship between the independent variable and the dependent variable, the less likely it is that the relationship is due to an extraneous variable. • 2: Temporality: It is logically necessary for a cause to precede an effect in time. • 3: Consistency: Multiple observations, of an association, with different people under different circumstances and with different measurement instruments increase the credibility of a finding.

13. Bradford Hill Criteria • 4: Theoretical Plausibility: It is easier to accept an association as causal when there is a rational and theoretical basis for such a conclusion. • 5: Coherence: A cause-and-effect interpretation for an association is clearest when it does not conflict with what is known about the variables under study and when there are no plausible competing theories or rival hypotheses. In other words, the association must be coherent with other knowledge.

14. Bradford Hill Criteria • 6: Specificity in the causes: In the ideal situation, the effect has only one cause. In other words, showing that an outcome is best predicted by one primary factor adds credibility to a causal claim. • 7: Dose Response Relationship: There should be a direct relationship between the magnitude of the risk factor (i.e., the independent variable) and severity of the disease variable (i.e., the dependent variable).

15. Bradford Hill Criteria • 8: Experimental Evidence: Any related research that is based on experiments will make a causal inference more plausible. • 9: Analogy: Sometimes a commonly accepted phenomenon in one area can be applied to another area. Hill, B.A. (1965). The environment and disease: Association or causation? Proceedings of the Royal Society of Medicine, 58, 295-300.

16. Exposure Evaluation Questions: • Is Agent Present? • Is there a Route of Exposure for Agent? (air, dust, water, food) • Did Agent get Into or On the Body? • If in the Body, did Agent Cause Effects? Questions 1 & 2: Answered by Industrial Hygienist Questions 3 & 4: Answered by Physician

17. Discussion