As I understand it lead paint in the US was a scourge in poor neighborhoods. Old lead paint tends to flake and small children love the taste of lead paint chips because it tastes sweet. 1950-1970's lead paint was a huge issue in poor neighborhoods.

Point I'd make is, often you see people trying or use epidemiological studies to try and prove some cause and effect. And this doesn't actually work very well. The world is filled with associations that have nothing to do with each other. However with lead the neurotoxic effects are fairly well understood in detail. As well as population exposure rates. So in this case epidemiological studies are confirming what one might well expect. Lead exposure ->