Much depends on whether Chernobyl is viewed as the result of a singular conjunction of technical, human and institutional failures or as the indicator of an incompressible risk residual connected with nuclear power. The latter figure was derived by a WHO Expert Group based on the linear no threshold methodology adopted by the International Commission on Radiological Protection. It corresponds to a 3-4% increase in the number of cancers that would have been likely to happen otherwise in the concerned groups.