Did removing lead from petrol spark a decline in crime?
I what some people here seemed to be missing, is this correlation isn't just lead was removed from the environment and 23 years later crime went down. It's that various areas has differing degrees of lead pollution and started reducing it at different times.The places that reduced lead pollution first, saw the drop in crime first, the places that reduced it later saw the drop later. The eras that initially had high levels of lead had a larger drop in crime than areas that always had a low level.And it's not just the USA either. The pattern holds pretty accurately for various nations around the world, like in Europe. Those who banned leaded fuel first, saw the drop in crime first, those who banned later, saw the drop later.And these nations had massively differing crime policies. Some nations increased prison sentences to try and deter crime, and crime went down. Some nations put a huge effort into reforming criminals, and crime went down. And some nations cut prison sentence, and crime went down.