Notable minimum value of relative risk recognized by Japanese epidemiologists and rule of proof in civil trial: questionnaire survey

Members of The Japanese Society of Cancer Epidemiology were questioned about relative risk in cancer epidemiology. The notable minimum value of relative risk recognized by the epidemiologists distributed from 1.1 to 5.0, and the mean and the standard deviation of the notable minimum value were 1.92 and 0.760. In civil litigation of United States a plaintiff must prove one's case by a "preponderance of evidence," which means that a causal relationship between risk factors and a health disturbance to a plaintiff is proved when relative risk is 2.0 or more. The mean value 1.92 of the notable minimum value of relative risk nearly corresponded to the relative risk 2.0, which indicates that opinion of Japanese epidemiologists did not disagree with the rule of the proof in civil litigation of United States. It is mentioned that the standard of the proof should be "high probability" based on "a high level of conviction in the judge's own mind" in Japanese civil trials, and that the "high probability" means that relative risk is 5.0 or more if we dare to quantify the vagueness. This value corresponded to the maximum value of the notable minimum relative risk in the questionnaire to the Japanese epidemiologists. In civil litigation of Japan, the standard of the proof based on epidemiological results may be more conservative than the opinion of Japanese epidemiologists.