Fifty Inventions That Shaped the Modern Economy

by Tim Harford

Half a century later, the government changed its mind: the Clean Air Act of 1970 began a process of gradually weaning cars of lead. And a couple of decades after that, the economist Jessica Reyes noticed something interesting: Rates of violent crime were starting to go down. There are many reasons this might have happened, but Reyes wondered: children’s brains are especially susceptible to chronic lead poisoning. Is it possible that kids who didn’t breathe leaded gasoline fumes grew up to commit less violent crime? Different U.S. states had phased out leaded gasoline at different times. So Reyes compared the dates of clean air legislation with subsequent crime data. She concluded that nationally over half the drop in crime—56 percent—was because of cars switching to unleaded gas.