Say what? Lead levels account for most of the variation in crime rates

Of all the explanations for crime rates -- demographics, prison term length, socioeconomics -- lead (yes, the metal) exposure levels have the most significant and best conserved correlation across eras and nations.

His data from multiple countries, which have different abortion rates, police strategies, demographics and economic conditions, indicate that lead is the only explanation that can account for international trends.

The previous query regarding causes was warranted.
More longitudinal imaging case comparisons here and here.