"THE MEANING OF RADIATION AT BIKINIATOLL" IT. ASSUMPTIONS Estimates of cancer and birth defect risks for the Bikini populations were based on a number of assumptions. Some of these assumptions re- sulted from consultation with other scientists including members of the BEIR committees. . Risk coefficients from BEIR-I were used because BEIR-III had 1. not been accepted by any U.S. government agency. We elected to use the values as given in BEIR-I rather than the revised values based on increased age of the population shown in Table V-4 of BEIR-I11. For estimates of cancer risk both the relative risk coefficient 2. and the absolute risk coefficient were used to give a range of estimated The absolute risk coefficient gives a lower value, is less vari- risk. able with the population and is not dependent upon the spontaneous cancer incidence, which is not known for the Bikini population. The relative risk coefficient gives a high value, but since it is based on the spontaneous cancer incidences, which is unknown for the Bikini population, it is probably less reliable than the estimates calculated from the absolute risk coefficients. For estimating increased cancer incidences, the bone marrow dose was used because it was slightly higher than the whole body dose. This probably introduced a small element of conservation. 3. 4. For estimating birth defects neither BEIR-I or BEIR-III is very clear about what is meant by parental dose, thus it is not clear whether birth defects should be based on the dose to one parent or both parents. In the latter case, the 30-year whole body dose would be doubled. We assumed the BEIR-I risk of 0.2% rem was based on both parents being irradiated. Also because we believed the risk coefficient from BEIR-I