BASES FOR CALCULATION OF RISK ESTIMATES USED IN "THE MEANING OF RADIATION AT BIKINI ATOLL" ..I. Assumptions (3) ——— —— (XG Estimates of cancer and birth defects 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. de Srtt 1. Risk coefficients from BEIR-I were used because BEIR-III had 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 jin Table V-4 of BEIR-III. ait 2. For estimates of cancer risk both the relative risk coef- ficient and the absolute risk coefficient were used to give a range of estimated risk. The absolute risk coefficient gives a lower value, is less variable 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. 3. 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 smal] element of conservation.