ORIGINAL ARTICLE Notable Minimum Value of Relative Risk Recognized by Japanese Epidemiologists and Rule of Proof in Civil Trial: Questionnaire Survey Minoru Sugita, Shaw Watanabe1, Masao Kanamori and Takashi Izuno Department of Environmental and Occupational Health, Toho University School of Medicine and 1Division of Epidemiology, National Cancer Center Research Institute, Tokyo, Japan (Received for publication on March 11, 1993) Abstract. 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. (Keio J Med 42 (3): 115-118, September 1993) Key words: epidemiologic data, health disturbance, civil litigation Introduction especially in United States.4 Relative risk is used in civil trials as a measure to judge whether alleged factors In analytical epidemiology we try to reveal quantitative caused health disturbances of plaintiffs in United States.1 relation between health disturbances and their risk We shall have to pay attention to notable minimum factors. Relative risk is an indicator which expresses value of relative risk for the civil courts in the near future strength of association between a health disturbance in Japan. and its risk factor. Attributable risk is an indicator which Meaning of relative risk is varied by the attributable expresses magnitude of a social problem with an increased risk value from the viewpoint of social medicine . In order incidence rate of a health disturbance due to its risk to detect the notable minimum value of relative risk factor. It gives a good idea of the impact that a success generally recognized by epidemiologists in Japan, mem ful prevention program of removing the risk factors bers of The Japanese Society of Cancer Epidemiology might have. were questioned about relative risk in cancer epidemiology In civil trials the role of epidemiology has become without consideration of the attributable risk. The results increasingly important,1 and there are cases which are of the survey were reported in the present study . influenced by evidence from epidemiological studies.2,3 Tools in the interface between law and epidemiology needed for resolving the issue have been developed 杉 田 稔,渡 辺 昌,金 森稚 夫,伊 津 野孝 Reprint requests to: Dr Minoru Sugita, Department of Environmental and Occupational Health , Toho University School of Medicine, 5-21-16 O mori nishi, Ota-ku, Tokyo 143, Japan 115 116 Sugita M, et al: Notable Minimum Value of Relative Risk Table 1 Translation of the Questionnaire Items about Relative Risk Recognized by Epidemiologists in Cancer Epidemiology Materials and Methods 1.1 to 5.0, and the mean and the standard deivation of the notable minimum value were 1.92 and 0.760. The Members of The Japanese Society Cancer Epide range of (Q2) the maximum relative risk was an area from miology were questioned about relative risk in cancer 10 to infinity, and the mean and the standard deviation epidemiology. Translation of the questionnaire items is of the maximum relative risk were 630 and 2240, and shown in Table 1. The subjects were questioned by mail those of (Q2') the common logarithm conversion value of from August through September in 1988. the maximum value were 1.93 and 0.673 (anti-logarithm conversion values to be 85.1 and 4.71), where infinity Results was calculated as 9999.9. The differences of means and the standard deviations between (Q1) the notable The questionnaires were distributed to 75 subjects minimum value and (Q2') the common logarithm con by mail, and 45 subjects (60.0%) responded to the version value of the maximum were small. The extent of questionnaire. (Q3) the notable minimum value of relative risk in a Minimums, maximums, means, standard deviations, sensitive sub-group distributed from 1.0 to 5.0, and the and numbers of subjects of (Q1) the notable minimum mean and the standard deviation of the value were 2.13 value of relative risk in cancer epidemiology recognized and 0.915. The mean of (Q1) the notable minimum value by epidemiologists, (Q2) the maximum value of relative of relative risk was slightly smaller than that (Q3) in risk which is known, (Q2') the common logarithm (base a sensitive sub-group. of logarithm si 10) conversion value of the above maxi Figure 1 shows histogram of (Q1) the notable minimum mum value, and (Q3) the notable minimum value of value of relative risk in cancer epidemiology, (Q2) the relative risk in a sensitive sub-group are shown in Table 2. maximum value of relative risk, or (Q3) the notable Table 2 indicates that (Q1) the notable minimum value minimum value of relative risk in a sensitive sub-group. of relative risk in cancer epidemiology distributed from Logarithm scale (breadth of each class to be •ã10 times) Table 2 Minimums, Maximums, Means, Standard Deviations, and Numbers of Subjects of (Q1) Notable Minimum Value of Relative Risk in Cancer Epidemiology, (Q2) Maximum Value of Relative Risk, (Q2') Common Logarithm Conversion Value of the Above Maximum Value, and (Q3) Notable Minimum Value of Relative Risk in a Sensitive Sub-group SD: standard deviation No.: number of subjectsa : •‡ was assigned to 9999.9 for calculation. b: •‡ was assigned to log109999 .9 for calculation. 117 Keio J Med 42 (3): 115-118, 1993 Q1. Notable Minimum Value of Relative Risk was used for (Q2) the maximum value of relative risk. (Total Number of Subjects: 40) Each histogram shows positive skewness of the distri bution, i.e. longer tail at the side of the large value. The histogram of (Q1) the notable minimum value of relative risk resembled closely that of (Q2) the maximum value of relative risk expressed by logarithm scale. As main cancer sites and their risk factors for maximum relative risk, lung cancer (9) and larynx cancer (6) caused by smoking and hepatocellular carcinoma (9) due to hepatitis B virus were listed by many epidemiologists. The numbers in the parentheses indicate numbers of epidemiologists. Discussion In epidemiology, relative risk is used as an indicator which expresses strength of association between a disease Q2. Maximum Value of Relative Risk and its risk factor, and attributable risk is used as an (Total Number of Subject: 38) indicator which expresses magnitude of a social problem with an increased incidence rate of a disease due to its risk factor. Significance of relative risk is affected by value of the attributable risk from the viewpoint of social medicine. In the questionnaire survey of the present study, the notable minimum value of relative risk in cancer epidemiology generally recognized by Japanese epidemiologists was investigated without consideration of the attributable risk. Attributable risk percent (AR%) is an indicator usually used in epidemiology. The meaning of AR% is the proportion of patients with a disease in the group that could be prevented by eliminating its risk factor. The calculation method of AR% value is AR%=(RR-1)/RR, where RR is relative risk value. Q3. Notable Minimum Value of Relative Risk in a Sensitive Sub-group The range of the notable minimum value of relative (Total Number of Subjects: 31) risk was 1.1-5.0 and the standard deviation was 0.760, which does not show that large difference of recognition about the notable minimum value of relative risk in cancer epidemiology among Japanese epidemiologists was detected. The mean of the notable minimum valae was 1.92, this value is slightly smaller than 2. The mean 1.92 for the notable minimum relative risk is corresponds to AR% 47.9%. Let us inquire these values from view point of civil court. In civil litigation of United States, a plaintiff must prove one's case by a "preponderance of evidence" rule.1,4.5 This criterion is a basic trend of the United States legal system.1,4,5 It is also termed the "more likely than not" rule,1,4,5 the "50.1 percent or more probability" rule,1,4,5 or the "reasonable medical certainty" rules "Preponderance of evidence" is d efined as "evidence of greater weight or more convincing than the evidence Fig 1 Histograms of the questions. which is offered in opposition to it ... 'preponderance' denotes a superiority of weight ."5 Therefore, in civil 118 Sugita M, et al: Notable Minimum Valueeof Relative Risk litigation of United States causal relationship between their recognition as a social problem. Therefore, it is risk factors and a disease to plaintiffs is proved when mentioned that useful information for civil trial was AR% is 50% or more i.e.