The cover story of the current issue of The Economist looks at the fall in crime rates and does its usual thorough job in covering the waterfront of factors contributing to this happy story. But they may have missed a big part of the story. There is some intriguing research that argues in favor of the conclusion that the decline in lead levels in the environment may have a significant but heretofore unrecognized role in the fall in crime. I’m surprised The Economist overlooked this; it’s the kind of exogenous factor that they typically love to highlight.
One of the better surveys of this hypothesis comes from Kevin Drum in Mother Jones magazine in January 2013. (Now I know what you’re thinking. Lefty Kevin Drum? Mother Jones?!?! But bear with this: as you’ll see by the close, James Q. Wilson credits this theory, and I’ll go with James Q. any day of the week.) Reviewing several studies widely scattered in time, space, and methodology, Drum summarizes:
It’s the only hypothesis that persuasively explains both the rise of crime in the ’60s and ’70s and its fall beginning in the ’90s. Two other theories—the baby boom demographic bulge and the drug explosion of the ’60s—at least have the potential to explain both, but neither one fully fits the known data. Only gasoline lead, with its dramatic rise and fall following World War II, can explain the equally dramatic rise and fall in violent crime.
Drum draws our attention to several academic papers on the subject, starting with Rick Nevin’s 1999 study published in Environmental Research that traced a close statistical correlation between changing lead levels and changing crime rates. As Drum summarizes Nevin’s findings, “he concluded that if you add a lag time of 23 years, lead emissions from automobiles explain 90 percent of the variation in violent crime in America. Toddlers who ingested high levels of lead in the ’40s and ’50s really were more likely to become violent criminals in the ’60s, ’70s, and ’80s.” Nevin returned to the issue several times over the last decade and has extended his research in several similar journal articles, which he summarizes in a PDF file on his website (www.ricknevin.com), “The Answer is Lead Poisoning.” Mindful of the axiom that “correlation does not equal causation,” in a new paper from January 2013 Nevin walks through nine factors that argue strongly for accepting a causative correlation in the case of lead and crime. (See Figure A below.)
Separate research of state-by-state lead levels and crime statistics by Amherst College economist Jessica Wolpaw Reyes arrives at the same conclusion as Nevin. Reyes reaches the specific conclusion that “changes in childhood lead exposure are responsible for a 56% drop in violent crime in the 1990s. . . children born in the 1980s, who experienced drastically lower lead exposure after the phase-out of lead from gasoline, may have been much less likely to commit crimes when they became adults in the late 1990s and early 2000s.”
While compelling, the super-numerate Jim Manzi cautions that confounding variables in these assessments come “way short of making a convincing case for spending $400 billion of taxpayer money” to remediate old houses with lead paint, as Drum, Nevin, and other advocates recommend. While agreeing that Nevins and Reyes are on to something significant, Manzi points out that with just a few changes of focus in what variables are included in the statistical analysis, much of Reyes’s lead-crime correlation disappears. Drum responded to Manzi, and Manzi returned service here. This issue clearly will play out further.
Regardless of how subsequent analysis of this thesis turns out, there’s a public choice angle to this captured well (but unwittingly I think) in Drum’s account:
Before he died last year, James Q. Wilson—father of the broken-windows theory, and the dean of the criminology community—had begun to accept that lead probably played a meaningful role in the crime drop of the ’90s. But he was apparently an outlier. None of the criminology experts I contacted showed any interest in the lead hypothesis at all.
Why not? Mark Kleiman, a public policy professor at the University of California-Los Angeles who has studied promising methods of controlling crime, suggests that because criminologists are basically sociologists, they look for sociological explanations, not medical ones. My own sense is that interest groups probably play a crucial role: Political conservatives want to blame the social upheaval of the ’60s for the rise in crime that followed. Police unions have reasons for crediting its decline to an increase in the number of cops. Prison guards like the idea that increased incarceration is the answer. Drug warriors want the story to be about drug policy. If the actual answer turns out to be lead poisoning, they all lose a big pillar of support for their pet issue. And while lead abatement could be big business for contractors and builders, for some reason their trade groups have never taken it seriously.