Epidemiological evidence showing an association between exposure to a substance and a disease in populations is admissible as circumstantial evidence of causation in an individual case, but a trial judge must evaluate the strength and quality of the studies — including the strength of association, consistency between studies, biological plausibility, and dose-response relationships. A modest increased risk ratio (such as 1.4 or 1.5-2.0) does not, without more, establish causation on the balance of probabilities. The balance of probabilities is not satisfied by evidence that establishes only a possibility of causation.
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