Removing Lead, Dropping Crime

Fourteen years ago, Prof Jessica Wolpaw-Reyes, an economist at Amherst College Massachusetts, was pregnant and doing what many expectant mothers do - learning about the risks to her unborn child's health. She started to read up on lead in the environment and, like Nevin before her, began pondering its link to crime.

"Everyone was trying to understand why crime was going down," she recalls. "So I wanted to test if there was a causal link between lead and violent crime and the way I did that was to look at the removal of leaded petrol from US states in the 1970s, to see if that could be linked to patterns of crime reduction in the 1990s."

Wolpaw-Reyes gathered lead data from each state, including figures for gasoline sales. She plotted the crime rates in each area and then used common statistical techniques to exclude other factors that could cause crime. Her results backed the lead-crime hypothesis.

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