Probably no simple answer, but here's a long paper I just found: https://pubs.aeaweb.org/doi/pdf/10.1257/089533004773563485 https://pubs.aeaweb.org/doi/pdf/10.1

Probably no simple answer, but here's a long paper I just found: https://pubs.aeaweb.org/doi/pdf/10.1257/089533004773563485 https://pubs.aeaweb.org/doi/pdf/10.1257/089533004773563485 Another famous hypothesis is the phasing out of lead fuel: https://en.wikipedia.org/wiki/Lead%E2%80%93crime_hypothesis https://en.wikipedia.org/wiki/Lead%E2%80%93crime_hypothesis