3.3.3 Risk Estimates The total life time excess risk to a population (all gender/age groups)for all types of stochastic effects combined, i.e., fatal and non-fatal malignancies, and severe genetic effects, associated with high dose and high-dose rate exposures to radiation, currently is estimated to be approximately 15 x 107 Sv' 7(26). The overall risk is estimated to be decreased by a factor of 2 or greater for low dose and low-dose rate exposures (26). The overall estimate of the excess life-time risk of radiogenic cancer is approximately 10 x 10° Sv' based on the natural rate in the control population (26). Estimates have been calculated for the risks of radiation-inducted site and type-specific cancers. Overall, the radiogenic cancerrisk estimate is greater among persons exposed at younger ages, and amongfemales, primarily because their baseline rates for cancers of the breast and thyroid are higher than those of males. The overall risk also is higher among populations with certain genetic defects, e.g., xeroderma pigmentosum,(2). As in the case of estimate of the risk for all stochastic effects combined (v.s.), the risk estimates for radiogenic cancers associated with exposures to radiation at low doses and low dose rates, are estimated to be lower by a factor of 2 or greater than those for high levels of radiation (26). 3.4 | Psychologica! Effects The psychological impact of radiation accidents on persons directly and indirectly involved in them has received greater attention in recent years than heretofore among the medical and scientific communities. Some experimental andclinical studies suggest that exposure to radiation may induce neurophysiological changes that are manifested clinically as altered psychological states among the exposed population. While this issue continues to be debated, there is evidence to suggest that radiophobia and the socioeconomic repercussions associated with serious radiation accidents may induce psychosomatic effects, even among minimally or non-exposed populations (30). * Sv = sievert = 1000 mSv;International System (SI) unit of dose equivalent in man. 1 Sv = 100 rem (conventional unit). 13