Get the Lead out.

In the Freakiest bit of Freakonomics, John Donohue and Steven Levitt in an article in 2001, proposed that violent crime in the USA dropped in the 90's because abortion had been legalized 18 years earlier.

The same pattern does not hold in the UK where abortion was legalized earlier and violent crime continues to rise (to a level much lower than the current US level of course).

A competing theory due to, I don't remember who, is that the decline in violent crimein rthe USA was caused by the shift away from leaded gasoline which began in 1973, the same year as Roe v Wade. Lead poisoning is known to cause people to be irritable and to risk becoming violent. The idea is that sub-poisoning exposure might cause violence too.

The UK began shifting to unleaded in 1986 13 years after the USA (don't click the link in the google search it is dead).

That would imply that violent crime should have peaked in the UK in 2004. Now I will check.

update:
OK UK peak (so far) seems to be 2005/6 (they don't seem to use solar year).

I shouldn't have tried to be so precise. The peak in the US youth violent crime rate was 1995 -- 22 years after the US began to remove lead (note unlike in the case of abortion the exact cohort affected by the change is not clear).

So moving 13 years forward gets to my new predicted peak in roughly 2008.

update 2: More from the home office (with dates I can understand)

Recorded violence against the person for July to September 2007 fell by 8% compared with the same period in 2006

This appears to be the very latest news.

It does seem to fit the lead theory as well as it possibly can, statistics from 2008 not being available yet.

update: Mark Thoma in person tells me who came up with this theory. Turns out I vaguely remembered reading about it on his blog (I might have read the article in teh Washington Post but I read economistsview much more than I read the Post). Embarassingly, I also inadvertently copied his title for my post.

Looks like the other countries have already been looked at, although the UK might not have been since, as a laggard in getting the lead out, their violent crime should be peaking about now.

Pulled back from comments.

Mark Thoma has left a new comment on your post "Get the Lead out. In the Freakiest bit of Freakon...":

You may already know about this:

http://economistsview.typepad.com/economistsview/2007/07/get-the-lead-ou.html

Research Links Lead Exposure, Criminal Activity, by Shankar Vedantam, Washington Post: 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. ...

Although crime did fall dramatically..., a broad range of scientific research has emerged ... to show that the mayor deserves only a fraction of the credit... The most compelling information has come from an economist in Fairfax 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 lead poisoning.

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 theory for fluctuations in the crime rate, and it is based on studies linking children's exposure to lead 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 ninety 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. ...

Many other theories have emerged to try to explain the crime decline. ... 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 fall of drug epidemics. ...

Most of the theories have been long on intuition and short on evidence. Nevin says his data not only explain the decline in crime in the 1990s, but the rise in crime in the 1980s and other fluctuations going back a century. His data from multiple countries, which have different abortion rates, police strategies, demographics and economic conditions, indicate that lead is the only explanation that can account for international trends.

Because the countries phased out lead at different points, they provide a rigorous test: In each instance, the violent crime rate tracks lead poisoning levels two decades earlier.

"It is startling how much mileage has been given to the theory that abortion in the early 1970s was responsible for the decline in crime" in the 1990s, Nevin said. "But they legalized abortion in Britain, and the violent crime in Britain soared in the 1990s. The difference is our gasoline lead levels...

Lead levels plummeted in New York in the early 1970s, driven by federal policies to eliminate lead from gasoline and local policies to reduce lead emissions from municipal incinerators. Between 1970 and 1974, the number of New York children heavily poisoned by lead fell by more than 80 percent... Lead levels in New York have continued to fall...

The later drop in violent crime was dramatic. In 1990, 31 New Yorkers out of every 100,000 were murdered. In 2004, the rate was 7 per 100,000 -- lower than in most big cities. The lead theory also may explain why crime fell broadly across the United States in the 1990s, not just in New York.

The centerpiece of Nevin's research is an analysis of crime rates and lead poisoning levels across a century. The United States has had two spikes of lead poisoning: one at the turn of the 20th century, linked to lead in household paint, and one after World War II, when the use of leaded gasoline increased sharply. Both times, the violent crime rate went up and down in concert, with the violent crime peaks coming two decades after the lead poisoning peaks.

Other evidence has accumulated in recent years that lead is a neurotoxin that causes impulsivity and aggression, but these studies have also drawn little attention. In 2001, sociologist Paul B. Stretesky and criminologist Michael Lynch showed that U.S. counties with high lead levels had four times the murder rate of counties with low lead levels, after controlling for multiple environmental and socioeconomic factors.

In 2002, Herbert Needleman, a psychiatrist at the University of Pittsburgh, compared lead levels of 194 adolescents arrested in Pittsburgh with lead levels of 146 high school adolescents: The arrested youths had lead levels that were four times higher.

"Impulsivity means you ignore the consequences of what you do," said Needleman, one of the country's foremost experts on lead poisoning, explaining why Nevin's theory is plausible. Lead decreases the ability to tell yourself, "If I do this, I will go to jail." ...

Within the field of neurotoxicology, Nevin's findings are unsurprising, said Ellen Silbergeld ... at Johns Hopkins University and the editor of Environmental Research. "There is a strong literature on lead and sociopathic behavior among adolescents and young adults with a previous history of lead exposure," she said.

Two new studies by criminologists Richard Rosenfeld and Steven F. Messner have looked at Giuliani's policing policies. They found that the mayor's zero-tolerance approach to crime was responsible for 10 percent, maybe 20 percent, at most, of the decline in violent crime in New York City. ...

Nevin's finding may even account for phenomena he did not set out to address. His theory addresses why rates of violent crime among black adolescents from inner-city neighborhoods have declined faster than the overall crime rate -- lead amelioration programs had the biggest impact on the urban poor. Children in inner-city neighborhoods were ... more likely to live in substandard housing that had lead paint and ... public housing projects were often situated near highways.

Chicago's Robert Taylor Homes, for example, were built over the Dan Ryan Expressway... Eighteen years after the project opened in 1962, one study found that its residents were 22 times more likely to be murderers than people living elsewhere in Chicago.

Nevin's finding implies a double tragedy for America's inner cities: Thousands of children in these neighborhoods were poisoned by lead in the first three quarters of the last century. Large numbers of them then became the targets, in the last quarter, of Giuliani-style law enforcement policies.