Ban on lead the cause of drop in crime?

Here is a quick overview about how the reduction of lead exposure in society could have contributed to the recent decline in crime rates:

One of the most fascinating questions in American sociology, political science, and public policy is the substantial decline in violent crime in America has been falling for two decades after a near-peak in 1991; the homicide rate hit a 50-year low last year despite the recession. There are a lot of interesting theories, none that (as far as I’ve read) is considered dominant. In November, Llewellyn Hinks-Jones wrote a compelling piece for the Atlantic about crime rates and the declining price of cocaine; there’s the evergreen broken-windows theory; Steven Levitt’s abortion theory (PDF); increasing incarceration rates; the destruction of massive public-housing complexes; improved trauma care; and many more. I was reminded of another one when reading up on public housing yesterday, thanks to a brief aside in Beryl Satter’s masterful Family Properties (emphasis mine):

The “peril to life and safety of the inhabitants” of slum buildings was often of a gruesome sort. Residents were injured on poorly lit stairways or ones with broken banisters. They were knocked out by falling plaster. They were scalded by the escaping steam of malfunctioning radiators. They perished in fires in buildings where fire escapes had collapsed from neglect. Their infants’ limbs were gnawed by rats. Each year approximately twenty-five children died from eating lead-filled paint chips. Others survived lead poisoning but were left mentally disabled.

Satter’s numbers come from a Chicago Daily News report from 1963. To put that in context, between 16 and 46 young Chicagoans died from accidents each year between 2002 and 2006, the leading cause of death in the 1-14 age group. In a 1962 Trib report, a board of health poison control pilot study found 35 deaths from 1959 to 1961: “Most of the victims were from 1 to 5 years old and came from rundown slum area buildings….” 465 cases were treated at County Hospital in those two years, and another 65 suffered severe brain damage…

That’s correlation, but what about cause? The great young science writer Jonah Lehrer explains the believed chain of causation from lead poisoning to violence (emphasis mine):

Here, for instance, is a recent PLOS study from the Cincinnati Lead Study, in which the blood lead level of babies born in poor areas of Cincinnati were repeatedly measured between 1979 and 1984. Twenty years later, the researchers tracked down these subjects and put them in MRI machines, allowing them to measure the brain volume of participants. The researchers found that exposure to lead as a child was linked with a significant loss of brain volume in adulthood, particularly in men. Furthermore, there was a “dose-response” effect, in which the greatest brain volume loss was seen in participants with the greatest lead exposure. What’s especially tragic is that the loss of volume was concentrated in the prefrontal cortex, a part of the brain closely associated with executive function and impulse control.

Several things come to mind:

1. Perhaps we simply need more scientific studies in order to sort this out yet a one cause answer to the drop in crime may be really difficult to find. Human behavior within a social context is complex.

2. I wonder if this hints at an already existing and likely to grow set of studies that discuss how everyday substances negatively affect us.

3. The person who is able to conclusively/definitively find the causes in the drop in crime will be either heralded, attacked from all sides, and perhaps both.

Drop in crime due to decreased lead exposure?

The crime rate in the United States is down again and people are looking for reasons why. Here is an interesting possible answer from James Q. Wilson: crime is down because people are exposed to less lead. This is how the reduction in lead would help:

In recent years, neuroscientists have made important progress in identifying the precise mechanisms by which lead exposure reduces impulse control…

While we can’t always control what we feel – many of our urges are ancient drives, embedded deep in the brain – we can control the amount of attention we pay to our feelings. When faced with a tempting treat, we can look away…

The tragedy of lead exposure is that it undermines one of the most essential mental skills we can give our kids, which is the ability to control what they’re thinking about. While the unconscious will always be full of impulses we can’t prevent, and the world will always be full of dangerous temptations, we don’t have to give in. We can choose to direct the spotlight of attention elsewhere, so that instead of thinking about the marshmallow we’re thinking about Sesame Street, or instead of thinking about our anger we’re counting to ten. And so there is no fight. We walk away.

This is an interesting argument. I suspect there is a bigger story that could be told about lead reduction over the years: Wilson hints at the background as the EPA announced a phased-in reduction in the lead in gasoline in late 1973 and lead was banned from paint in 1977. These facts are taken for granted now but I imagine these were public health announcements that created some discussion at the time, particularly from industry lobbying groups.

Is there a way to test the lead hypothesis by looking at a comparison group?

If this turned out to be a primary factor in the reduction of crime, how would public officials, police officers, and the public work with this information?