Scientific and legal standards of statistical evidence in toxic tort and discrimination suits

Abstract

Many legal disputes turn on scientific, especially statistical, evidence. Traditionally scientists have accepted only that statistical evidence which satisfies a 95 percent (or 99 percent) rule — that is, only evidence which has less than five percent (or one percent) probability of resulting from chance.

The rationale for this rule is the reluctance of scientists to accept anything less than the best-supported new knowledge. The rule reflects the internal needs of scientific practice. However, when uncritically adopted as a rule for admitting legal evidence, the seemingly innocuous 95 percent rule distorts the balance of interests historically protected by the legal system. In particular, plaintiffs in toxic tort and employment discrimination suits are effectively held to a heavier burden of proof in showing that their injuries were more probably than not caused by the defendant's actions. The result is that too many victims of toxic torts or employment discrimination cannot win legal redress for their injuries.

Proposals to adopt stringent scientific rules of evidence thus implicate significant philosophical issues about the relation of evidence to belief and to practical action. The underlying objectives of the tort law system are not those of scientific practice, and each set of objectives has standards of evidence specific to it.