Yesterday I returned to banging the (Kevin) drum about the pernicious effects of environmental lead. Both a note from a reader and comments elsewhere about Kevin’s latest post suggest that an earlier post of mine had created confusion.
Here’s the note:
Mark, in your latest post, you seem to be believing the lead hypothesis for violent crime again. But here I thought you said that Phil Cook changed your mind. Are there new data that tipped you back, or is there a hole in Cook’s argument?
There are two different claims here:
- Lead causes crime, and the effect size is large.
- Decreasing lead exposure was the primary cause of the crime decline that started in 1994.
#1 is certainly true, and nothing Cook has written or said contradicts it. We have both statistical evidence at the individual level and a biological understanding of the brain functions disrupted by lead.
Cook convinced me that #2 is not true, or at least is not the whole story, because the decline happened in all cohorts while lead exposure deceased only for the younger cohorts. You can still tell plausible stories about how the young’uns drove the homicide wave of the late 1980s/early 1990s and that less violent subsequent cohorts of young’uns reduced the overall level of violence, but that’s not as simple a story. In a world of many interlinked causes and both positive and negative feedbacks, the statement “X% of the change in A was caused by a change in B” has no straightforward empirical sense.
So I’m absolutely convinced that lead is criminogenic, in addition to doing all sorts of other personal and social harm, and strongly suspect that further reductions in lead exposure (concentrating on lead in interior paint and lead in soil where children play) would yield benefits in excess of their costs, even though those costs might be in the billions of dollars per year. What’s less clear is how much of the crime increase starting in the early 1960s and the crime decrease starting in the early 1990s (and the rises and falls of crime in the rest of the developed world) should be attributed to changes in lead exposure.
The original point of yesterday’s post stands: When you hear people complaining about environmental regulation, what they’re demanding is that businesses should be allowed to poison children and other living things. No matter how often they’re wrong about that – lead, pesticides, smog, sulphur oxides, chlorofluorocarbons, estrongenic chemicals – they keep on pretending that the next identified environmental problem – global warming, for example – is just a made-up issue, and that dealing with it will tank the economy. Of course health and safety regulation can be, and is, taken to excess. But the balance-of-harms calculation isn’t really hard to do. And the demand for “corporate free speech” is simply a way of giving the perpetrators of environmental crimes a nearly invincible political advantage over the victims.