Lead and crime: a hole in the theory

Kevin Drum, whose “Criminal Element” essay linking violence rates to lead exposure has been (as it deserves to be) extraordinarily influential, links to a BBC story in which a more-than-usually-dim criminologist explains that he disbelieves in the lead-crime link because all biological explanations of crime are outside “the mainstream” (presumably meaning “the mainstream of criminological research”). Kevin is right to say that the multiple levels of evidence for the lead-crime link (brain-imaging work, case-control studies at the individual level, studies of crime changes in neighborhoods that suffered greater and lesser increases in lead exposure after WWII and decreases in lead exposure after the mid-1970s, and cross-national studies) deserve more than a casual blow-off. It’s not, after all, as if “mainstream” criminology had a bunch of well-worked out causal theories with proven predictive power.

Like Kevin, I’ve been frustated that the evidence about lead hasn’t led to more action, if only some serious experimental work removing lead from randomly selected buildings or neighborhoods and then doing developmental measurements on the childen in the chosen areas compared to children in control areas. And I was puzzled when I heard that the hyper-sensible Phil Cook of Duke was among the skeptics.

Alas, Phil seems to have good reason to raise questions, especially about the ultra-strong claims sometimes heard about the percentage of the crime drop since 1994 attributable to changes in lead exposure. (Note that in a system with multiple positive feedbacks, the change-attribution factors needn’t sum to unity, so the claim that “the change in X accounts for 90% of the change in Y” is dubious on its face.)

Cook writes:

My skepticism about the “lead removal” explanation for the crime drop stems from the same source as my skepticism about the Donohue-Levitt explanation in terms of abortion legalization. They have an exact parallel to the previous explanations for the surge in violence of the late ‘80s by John DiIulio and others. The focus in both cases is the character of the kids – the belief that during the 80s the teens were getting “worse,” and during the 90s they were getting “better.” Even a fairly casual glance at the data demonstrates that whatever the cause of the crime surge, and then the crime drop, it was not associated with particular cohorts. It was an environmental effect – 10 cohorts were swept up in the crime surge simultaneously, and the drop has the same correlated pattern.

There is a natural inclination to assume that the reason the murder rate is increasing is because there are more murderers, and the reason we have fewer is that there are fewer murderers. It’s not that I rule out such explanations – I’m open to the idea of lead removal and abortion legalization – it’s just that I don’t think it explains the actual pattern of the youth violence epidemic, either up or down. More generally, my instinct is to look to the social and economic environment to explain large shifts in population outcomes.

Here’s Cook’s paper with John Laub.

Now, since youth violence surely has impacts on adult violence, finding that all the cohorts decreased their violence at the same time doesn’t quite rule out the idea that the younger cohorts were largely driving the train. And those brain-imaging, case-control, neighborhood, and cross-national results are still out there. But Cook’s objection remains a powerful one: the theory predicts that we should have seen the crime declines specifically in the birth cohorts exposed to less lead, and that’s not what we saw in fact.

I’d still like to see some experimental work to figure out how much additional lead removal would turn out to be cost-justified (with crime-reduction benefits a significant, but but not the dominant, part of the benefit story), but the simple story “Crime declined because lead declined” now has a major hole in it. That’s too bad, because attempts to find the relevant social and economic causes haven’t gotten very far. To my mind, the crime boom that started in the late 1950s or early 1960s and the crime bust that started in the mid- 1990s (and other large-scale, decades-long swings up and down in crime rates elsewhere) remain largely unexplained in retrospect, as they were entirely unpredicted in prospect.

Footnote And that, of course, is the difference between science and policy analysis on the one hand and mere advocacy on the other. Of course scientists and analysts are influenced by their values and prejudices. I don’t pretend that Jessica Reyes’s work didn’t make me happy or that Cook’s response doesn’t make me sad. The lead-crime story fits all my political prejudices, as well as my taste for simple and surprising explanations with clear policy implications. And I’ve been a loud advocate for it. But I don’t want to believe it if it isn’t true.

Getting the (remaining) lead out

Shorter Kevin Drum:

1. Lead is remarkably nasty stuff. In minuscule quantities (measured in the single digits of micrograms per decliter of blood) it damages both IQ and the capacity for self-command.

2. The rise of lead exposure from gasoline, and its subsequent decline, accounts for a large share of the crime boom of 1960-90 and the crime decline that started in 1994.

3. Children are still being exposed to lead from two major sources: residual lead in soil, and lead paint in homes, especially window-frames.

4. Substantially eliminating those sources of exposure would require a one-time expenditure of about $400 billion. (That sounds like a lot of money, until you look at Treasury bond rates and translate it to $12 billion a year.)

5. The return on that investment would be at least in the high tens of billions of dollars per year.

Kevin’s piece, the cover story in the current Mother Jones, is a model of science/policy journalism. He carefully chases down both the biology and the social science supporting the claims about the effects of lead, identifies the main remaining sources, and documents the abatement processes, with cost estimates. (The quantification of benefits is mostly hand-waving; neither the outcome predictions nor the valuations are convincing. But it’s more than adequate to show that the benefit-cost analysis would come out hugely positive.)

It remains to be seen whether a crime-control and educational initiative that doesn’t fit the intellectual categories or feed the budgets of the criminal-justice and educational systems can obtain any political purchase. The answer so far seems to be no.

Getting the lead out

Kevin Drum makes a strong case for spending the money to remove the remaining sources of environmental lead: old lead paint and residential water pipes. Eliminating lead paint an lead pipes each would have costs in the tens-of-billions range. In each case that would mean either (1) requiring private parties to spend substantial amounts of money or (2) spending substantial amounts of public money to fix up private property, somewhat unfairly to those who prudently spent their own money to fix it.  But neither problem could possibly justify allowing the ongoing damage from lead exposure; those are one-time expenditures, and the flow of damage from lead is a continuing cost.

One source Kevin doesn’t mention is smelters, which used to be a major source. I’m not current enough to know whether most of the smelter business has moved abroad, but I’m sure there are still some domestic smelters, and they’re inevitably bad news on the lead front.

As Kevin notes, one consequence of lead exposure is higher crime: lead reduces IQ and also specifically attacks some of the brain functions that support self-control. But consider what a horse-laugh a politician would get if he listed de-leading among his crime-control proposals.