Observational vs Experimental Studies Math Example 2

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Example 2

hard
An observational study finds smokers have 10x the lung cancer rate of non-smokers. Critics say this could be due to a genetic confounder that causes both smoking and cancer. How did scientists eventually establish smoking CAUSES cancer?

Solution

  1. 1
    Challenge: cannot randomly assign smoking to humans (unethical); strong observational evidence exists but critics could invoke confounders
  2. 2
    Methods used to establish causation despite observational limits: (1) dose-response relationship (more smoking → more cancer); (2) temporality (smoking precedes cancer); (3) animal experiments (assigned smoking, saw cancer); (4) biological mechanism identified; (5) multiple independent study designs converge on same conclusion
  3. 3
    Bradford Hill criteria: strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment, analogy
  4. 4
    Conclusion: the weight of converging evidence from multiple approaches established causation beyond reasonable doubt

Answer

Causation established via dose-response, temporality, animal experiments, biological mechanism, and multiple converging study designs.
When randomized experiments are impossible (ethical issues, long time horizons), causation can be established through multiple complementary lines of evidence. The Bradford Hill criteria provide a framework for causal inference in observational research.

About Observational vs Experimental Studies

An observational study records data without imposing treatments, while an experiment deliberately manipulates a variable. Only experiments with random assignment can establish causation; observational studies can only show association.

Learn more about Observational vs Experimental Studies →

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Example 4 hard

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