Lead exposure causes crime, economist says

Rudy Giuliani never misses an opportunity to remind people about his track record in fighting crime as mayor of New York City from 1994 to 2001.

"I began with the city that was the crime capital of America," Giuliani, now a candidate for president, recently told Fox's Chris Wallace. "When I left, it was the safest large city in America. I reduced homicides by 67 percent. I reduced overall crime by 57 percent."

While crime did fall dramatically in New York during Giuliani's tenure, a broad range of scientific research has emerged in recent years to suggest the former mayor deserves only part of the credit that he claims. The most compelling information has come from an economist in Fairfax, Va., who has argued in a series of little-noticed papers that the "New York miracle" was caused by local and federal efforts decades earlier to reduce exposure to lead.

The theory offered by the economist, Rick Nevin, is that lead poisoning accounts for much of the variation in violent crime in the United States. It offers a unifying new neurochemical explanation for fluctuations in the crime rate and is based on studies linking exposure to lead in children with violent behavior later in their lives.

What makes Nevin's work persuasive is that he has shown an identical, decades-long association between lead poisoning and crime rates in nine countries.

"It is stunning how strong the association is," Nevin said. "Sixty-five to 90 percent or more of the substantial variation in violent crime in all these countries was explained by lead."

Through much of the 20th century, lead in U.S. paint and gasoline fumes poisoned toddlers as they put contaminated hands in their mouths. The consequences on crime, Nevin found, occurred when poisoning victims became adolescents. Nevin does not say lead is the only factor behind crime, but he says it is the biggest factor.

Giuliani's presidential campaign declined to address Nevin's contention that the former mayor merely was at the right place at the right time. But William Bratton, who served as Giuliani's police commissioner and initiated many of the policing techniques credited with reducing the crime rate, dismissed Nevin's theory as absurd. Bratton and Giuliani instituted harsh measures against quality-of-life offenses, based on the theory that addressing minor offenses would head off more serious crimes.

Other theories

Many other theories have emerged to explain the crime decline. In the 2005 book "Freakonomics," Steven D. Levitt and Stephen J. Dubner said the legalization of abortion in 1973 had eliminated "unwanted babies" who would have become violent criminals. Other experts credited lengthy prison terms for violent offenders, or demographic changes, socioeconomic factors, and the rise and fall of drug epidemics. New theories emerged as crime rates inched up in recent years.

Most of the theories have been long on intuition and short on evidence. Nevin's data attempt to explain both the decline in crime in the 1990s and also the rise in crime in the 1980s, as well as other fluctuations going back a century. His data from multiple countries, which have different abortion rates, police strategies, demographics and economic conditions, suggest lead is the only explanation that can account for international trends.

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