Interpreting causality in the health sciences Federica Russo & Jon Williamson Philosophy, University of Kent
Causality and probability  in  the sciences <ul><li>An ongoing project at Kent </li></ul><ul><li>www.kent.ac.uk/secl/philo...
Overview <ul><li>Two types of evidence </li></ul><ul><ul><li>Probabilistic </li></ul></ul><ul><ul><li>Mechanistic </li></u...
Probabilistic evidence <ul><li>Observed dependencies  </li></ul><ul><li>in a range of similar studies </li></ul><ul><li>Co...
Mechanistic evidence <ul><li>Biomedical mechanisms </li></ul><ul><ul><li>Chemical reactions, electric signals,  </li></ul>...
We need both types of evidence <ul><li>Semmelweis and puerperal fever </li></ul><ul><ul><li>He had statistics but the link...
A classic: Bradford Hill’s criteria <ul><li>Strength of association </li></ul><ul><li>Temporality </li></ul><ul><li>Consis...
Contemporary medicine: IARC <ul><li>IARC reviews published studies </li></ul><ul><li>Assessment of causality depends on: <...
Monistic accounts won’t do <ul><li>Mechanistic accounts </li></ul><ul><ul><li>Causal processes intersect with each other  ...
Pluralistic accounts won’t do … either <ul><li>Uniformity of causal language: </li></ul><ul><li>A  single  notion of cause...
The way out: epistemic causality <ul><li>Rational causal beliefs: </li></ul><ul><ul><li>The agent’s evidence determines  <...
Constraints on causal beliefs <ul><li>The agent’s causal beliefs should account  </li></ul><ul><li>for all known dependenc...
An application: epistemic causality in cancer science <ul><li>Dataset of clinical observations of past patients </li></ul>...
To sum up <ul><li>The health sciences need and employ two types of evidence </li></ul><ul><li>Monistic accounts won’t do <...
To conclude … and to research ahead <ul><li>There is a key distinction between </li></ul><ul><ul><li>Evidence  from which ...
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Interpreting Causality

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Interpreting Causality

  1. 1. Interpreting causality in the health sciences Federica Russo & Jon Williamson Philosophy, University of Kent
  2. 2. Causality and probability in the sciences <ul><li>An ongoing project at Kent </li></ul><ul><li>www.kent.ac.uk/secl/philosophy/jw/2006/CausalityProbability.htm </li></ul><ul><li>In the sciences </li></ul><ul><li>About probability </li></ul><ul><ul><li>We defend an </li></ul></ul><ul><ul><li>ObjectiveBayesian-cum-Frequency interpretation </li></ul></ul><ul><li>About causality </li></ul><ul><ul><li>We defend an epistemic interpretation </li></ul></ul>
  3. 3. Overview <ul><li>Two types of evidence </li></ul><ul><ul><li>Probabilistic </li></ul></ul><ul><ul><li>Mechanistic </li></ul></ul><ul><li>Against causal monism </li></ul><ul><li>Against causal pluralism </li></ul><ul><li>The case for epistemic causality </li></ul>
  4. 4. Probabilistic evidence <ul><li>Observed dependencies </li></ul><ul><li>in a range of similar studies </li></ul><ul><li>Coherent results </li></ul><ul><li>Tests for stability </li></ul><ul><li>in structural models </li></ul><ul><li>… </li></ul>
  5. 5. Mechanistic evidence <ul><li>Biomedical mechanisms </li></ul><ul><ul><li>Chemical reactions, electric signals, </li></ul></ul><ul><ul><li>alterations at the cellular level, … </li></ul></ul><ul><li>A plausible (physiological) link </li></ul><ul><li>from the cause to the effect </li></ul>
  6. 6. We need both types of evidence <ul><li>Semmelweis and puerperal fever </li></ul><ul><ul><li>He had statistics but the link wasn’t accepted </li></ul></ul><ul><ul><li>till backed with the mechanism </li></ul></ul><ul><li>Helicobacter pylory </li></ul><ul><ul><li>The causal relation was hypothesised </li></ul></ul><ul><ul><li>based on probabilistic evidence and </li></ul></ul><ul><ul><li>accepted when backed with the mechanism </li></ul></ul>
  7. 7. A classic: Bradford Hill’s criteria <ul><li>Strength of association </li></ul><ul><li>Temporality </li></ul><ul><li>Consistency </li></ul><ul><li>Theoretical plausibility </li></ul><ul><li>Coherence </li></ul><ul><li>Specificity in the causes </li></ul><ul><li>Dose response relationship </li></ul><ul><li>Experimental evidence </li></ul><ul><li>Analogy </li></ul>
  8. 8. Contemporary medicine: IARC <ul><li>IARC reviews published studies </li></ul><ul><li>Assessment of causality depends on: </li></ul><ul><ul><li>Presence of a plausible mechanism </li></ul></ul><ul><ul><li>Probabilistic evidence </li></ul></ul><ul><ul><li>(e.g. frequencies, risks) </li></ul></ul>
  9. 9. Monistic accounts won’t do <ul><li>Mechanistic accounts </li></ul><ul><ul><li>Causal processes intersect with each other </li></ul></ul><ul><ul><li>in interactive forks </li></ul></ul><ul><li>Probabilistic accounts </li></ul><ul><ul><li>Causes make a difference </li></ul></ul><ul><ul><li>in the probability of the effect </li></ul></ul><ul><ul><li>(ceteris paribus) </li></ul></ul><ul><li>Problem: </li></ul><ul><li>Neither can handle the dual aspect </li></ul><ul><li>of causal epistemology </li></ul>
  10. 10. Pluralistic accounts won’t do … either <ul><li>Uniformity of causal language: </li></ul><ul><li>A single notion of cause is used </li></ul><ul><li>The pluralist rebuts: </li></ul><ul><ul><li>A mechanistic cause 1 </li></ul></ul><ul><ul><li>A probabilistic cause 2 </li></ul></ul><ul><ul><li>Different meanings of cause </li></ul></ul><ul><ul><li>But each refers to a single concept! </li></ul></ul><ul><li>Therefore, the pluralist has </li></ul><ul><li>twice as the problems of the monist! </li></ul>
  11. 11. The way out: epistemic causality <ul><li>Rational causal beliefs: </li></ul><ul><ul><li>The agent’s evidence determines </li></ul></ul><ul><ul><li>which beliefs to adopt </li></ul></ul><ul><ul><li>A causal relation is the set of causal beliefs </li></ul></ul><ul><ul><li>that an agent with total evidence </li></ul></ul><ul><ul><li>should adopt </li></ul></ul>
  12. 12. Constraints on causal beliefs <ul><li>The agent’s causal beliefs should account </li></ul><ul><li>for all known dependencies </li></ul><ul><li>that are not already accounted for </li></ul><ul><li>by non-causal dependencies </li></ul><ul><li>The agent’s causal beliefs should be </li></ul><ul><li>compatible with other knowledge </li></ul><ul><li>The agent should not have causal beliefs </li></ul><ul><li>that are not warranted by her evidence </li></ul>
  13. 13. An application: epistemic causality in cancer science <ul><li>Dataset of clinical observations of past patients </li></ul><ul><li>Dataset of observations at molecular level </li></ul><ul><li>Probabilistic evidence </li></ul><ul><li>Knowledge of biological mechanisms </li></ul><ul><li>Mechanistic evidence </li></ul><ul><li>Knowledge of semantic relations between variables </li></ul><ul><li>Pro/contra mechanistic evidence </li></ul>
  14. 14. To sum up <ul><li>The health sciences need and employ two types of evidence </li></ul><ul><li>Monistic accounts won’t do </li></ul><ul><li>Pluralistic accounts won’t do either </li></ul><ul><li>The epistemic account succeeds </li></ul>
  15. 15. To conclude … and to research ahead <ul><li>There is a key distinction between </li></ul><ul><ul><li>Evidence from which we draw causal conclusions </li></ul></ul><ul><ul><li>and the concept of cause </li></ul></ul><ul><li>A single epistemic concept suits </li></ul><ul><li>the case of the health sciences </li></ul><ul><li>… and possibly the social and natural sciences too </li></ul>

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