By now, you've all read my story about the link between the decline of leaded gasoline and the decline of violent crime, right? Here's an update from an unexpected source: the state of São Paulo in Brazil. Obviously the United States isn't the only place that got rid of leaded gasoline, which means the United States isn't the only place that should have seen declines in violent crime. But other countries made the switch at different times, which means their declines in violent crime should also have taken place at different times. Rick Nevin has done a lot of work...