Many NEI NN readers here know that there are two competing theories on radiation: linear no-threshold (LNT) and hormesis. For those who don't, the LNT theory basically says that there is no safe dose of radiation whereas the hormesis theory says small doses of radiation are safe and that there is a threshold before radiation becomes harmful. Both are highly debatable but the latter makes a stronger case - at least in my opinion. (US nuclear plants, however, are regulated under the LNT theory.)
One of the best analogies that explains the LNT theory comes from a comment made by DV82XL over at Physical Insights:
If the LNT were applied to falling as it is to radiation, we might note that 100 percent of those falling onto concrete from 100 feet are killed, but only 50 percent of those falling from 50 feet die. With these data we would linearly extrapolate to say that 10 percent falling from 10 feet and one percent of those falling from one foot would die. Armed with this “linear no-threshold falling theory,” we could confidently assert that jumping rope should be banned on all school playgrounds since statistically anyone making 100 one-foot jumps would die.Hat tip to Luke Weston.