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.
Lead paint was banned in 1972; between 1970 and 1973, the Trib reported that 18 cases of lead poisoning had been traced to buildings under one ownership alone. According to a 1980 Trib piece by Anne Keegan, Chicago didn't see any lead fatalities among children from 1974 through 1980, when poisoning from lead paint killed a toddler on South Ridgeland.
A measure of America's success in lead abatement can be seen in the decrease in the CDC-determined cutoff for childhood lead poisoning over time:
But the problem has seemed to be diminishing, based on the old standard. In 2009, researchers reported that 1.4 percent of young children had elevated lead levels in their blood in 2004, the latest data available. That compares with almost 9 percent in 1988.
The lead poisoning threshold was last changed in 1991. The proposed level of 5 micrograms was calculated from the highest lead levels seen in a comprehensive annual U.S. health survey. The panel recommended that it be reassessed every four years.
Some of this can be attributed to the lead-paint ban; some of it, to the ban of leaded gasoline in 1986, after more than six decades of use. In his epic Nation article "The Secret History of Lead," Automobile Magazine New York bureau chief Jamie Lincoln Kitman ran the numbers:
According to a 1988 report to Congress on childhood lead poisoning in America by the government's Agency for Toxic Substances and Disease Registry, one can estimate that the blood-lead levels of up to 2 million children were reduced every year to below toxic levels between 1970 and 1987 as leaded gasoline use was reduced. From that report and elsewhere, one can conservatively estimate that a total of about 68 million young children had toxic exposures to lead from gasoline from 1927 to 1987.
The bans on leaded gasoline and lead paint have also provided an interesting data set for social scientists:
The centerpiece of [Rick] 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.
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 the ones most likely to be poisoned by lead, because they were more likely to live in substandard housing that had lead paint and because public housing projects were often situated near highways.
Chicago's Robert Taylor Homes, for example, were built over the Dan Ryan Expressway, with 150,000 cars going by each day. 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.
After that Washington Post piece came out, Steven Levitt expressed skepticism of Nevin's work, coming in part from his own struggles to find a more fine-grained local correlation. But Levitt found more persuasive evidence in an NBER working paper from Jessica Wolpaw Reyes of Amherst, "Environmental Policy as Social Policy? The Impact of Childhood Lead Exposure on Crime" (PDF). Reyes looked at state-level data, and came away with similar conclusions:
The elasticity of violent crime with respect to childhood lead exposure is estimated to be approximately 0.8. This implies that, between 1992 and 2002, the phase-out of lead from gasoline was responsible for approximately a 56% decline in violent crime. Results for murder are not robust if New York and the District of Columbia are included, but suggest a substantial elasticity as well.
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.
Last year James Q. Wilson, the prominent conservative political scientist and co-inventor of the broken-windows theory, addressed one of the challenges criminologists have faced as violent crime declined during the recession, going back to the research of University of Chicago Nobel Prize winner Gary Becker:
The economist Gary Becker of the University of Chicago, a Nobel laureate, gave the standard view its classic formulation in the 1960s. He argued that crime is a rational act, committed when the criminal's "expected utility" exceeds that of using his time and other resources in pursuit of alternative activities, such as leisure or legitimate work. Observation may appear to bear this theory out. After all, neighborhoods with elevated crime rates tend to be those where poverty and unemployment are high as well.
Wilson goes on to check off a list of economic indicators; unsurprisingly, they're all bad. He also runs through a list of societal changes—data-driven policing, the rise of marijuana use over cocaine, the decline in environmental lead exposure—and find them to be good. To this, he adds an odd cultural argument:
The cultural argument may strike some as vague, but writers have relied on it in the past to explain both the Great Depression's fall in crime and the explosion of crime during the sixties. In the first period, on this view, people took self-control seriously; in the second, self-expression—at society's cost—became more prevalent. It is a plausible case.
I dunno. And in fairness to Wilson, he doesn't either, leaving the cultural arguments to the novelists and biographers. But the scientists might have something to contribute to the poets. After all, the theory is that lead exposure leads to reduced self-control, which reduces the need to explain crime as a rational act—lead poisoning as a disease of mass irrationality. if the studies on lead continue to bear out, Wilson's offhand statement might be more true, or at least more quantifiable, than he thinks.
Photograph: Editor B (CC by 2.0)