Epidemiology and civil trials]

The role epidemiology in courts has become increasingly important both in the United States and in Japan, especially in the field of product liability. In the United States, attributable risk percent (AR%) is used in civil trials as a measure to judge whether alleged factors caused health disturbances of plaintiffs. Most epidemiologists believe that an AR% of more than 50%, ie, relative risk more than 2, supports causality of alleged factors, because "preponderance of evidence" is regarded as a fundamental legal rule in the United States. In Japan, judges in courts require a more strict standard for proof of facts, which means that a much higher AR% may be needed to convince judges. The role of epidemiologists in courts may be to show a plausible range of AR%, based on design, execution, and analysis of quoted epidemiologic studies. Standards for accepting plaintiffs' allegation should be discussed in the legal framework of Japan.