This is the fourth in a series from Dana Goldstein of the Justice Lab at The Marshall Project, Top 10 (Not Entirely Crazy) Theories Explaining the Great Crime Decline:
The lead hypothesis
This is perhaps the trendiest crime decline hypothesis in 2014, and it was the subject of an entire session of the National Academy roundtable’s work. The effect of lead on children’s brains has been well documented: Exposure to the chemical causes aggressive behavior and cognitive delays. In the wake of the 1970 Clean Air Act, lead was removed from gasoline and, increasingly, from paint.
Economist Jessica Reyes estimates that phasing out lead was responsible for 56 percent of the reduction in violent crime (although she could find no relationship between lead and property crime). Experts still disagree about how plausible it is that lead alone could have been responsible for such a massive portion of the crime drop. “It’s fair to say that our assessment of this hypothesis is ‘case not proved’—or at least ‘not yet proved,’ ” Rosenfeld said