Another indication that the effects of prenatal stress are not just caused by genetic continuity are the group of studies that have studied children of mothers exposed to acute disasters. These have included a Canadian ice storm , the September 2011 attacks and Chernobyl . With these ‘natural or man-made experiments’, as for example in the ice storm study, the level of stress was objectively assessed, and the exposure was of a specific duration. This reduces the confounding effects of pre-existing emotional problems and genetic