alt Hacker News> after the atomic bombing of Hiroshima, some people who would've received a relatively small dose of radiation seemed to have a slightly lower cancer risk than people who wouldn't have received any additional radiation.
What if this is survivorship bias selecting for some common trait that correlates with better radiation tolerance and lower cancer risk (like age).
IIRC, it's based on the distance from the blast radius. The confounding thing about it is the fact that there is apparently a range of distance from the explosion where people have lower incidence of cancer than people who were even further way.
That seems hard to explain.