NOTE 14 RISK FACTORS The recent revisions in dosimetry for Japanese bomb survivors have indicated that the risk factor for cancer mortality of 1 x 107‘ should be raised 2 - 10-fold (Shimizu et al 1987; Preston and Pierce 1987). The Japanese experience, however, was based on high dose, high dose-rate exposure, whereas the Rongelap experience under discussion is very low dose and very low dose-rate. The difference in dose-rate involves a factor downwards of 3 - 10-fold, and as a result the two changes cancel one another. To be on the safe side, flowever, I have chosen to raise the old BEIR factor from 1 to 2.5 x 10°¢. The matter is presently under discussion by the United Nations Scientific Committee on the Effects of Atomic Radiations, which is preparing a report for the International Committee on Radiation Protection. 82 9000689