Epidemiology and the Law

Summary

Epidemiological evidence is sometimes adduced in an attempt to prove that an exposure caused a particular claimant to suffer a disease. This attempt has been fraught with legal difficulty, much of it grounded on confusion about the epistemic force of epidemiological evidence. In this chapter we survey existing legal positions on the use of epidemiological evidence and find them confused. Progress is almost impossible until a clear distinction is made between what epidemiological evidence says and what it shows. The answer to the former question is not difficult. Given certain assumptions, epidemiological evidence can estimate a lower bound on the probability that the exposure was a cause of a given claimant’s case of disease. The answer to the latter question is more difficult, but on analysis it is clear that epidemiological evidence cannot be regarded as entirely unpersuasive in the legal context. One dramatic consequence of such an attitude would be the erroneous use of other kinds of evidence that clearly are relevant, such as medical tests. So in the right circumstances, epidemiological evidence can be used to prove specific causation to the applicable legal standard.¹