Sunday, July 08, 2007

Lead Exposure And Crime

An interesting article in the Washington Post discusses some new research on the correlation between childhood exposure to lead and increased propensity to crime in adulthood. Further on in the article one expert notes that lead exposure has been found to be associated with worse impulse control in general, and that could explain the correlation.

On the other hand, lead exposure also correlates with socioeconomic class, because poorer areas are more likely to have buildings with old, peeling lead paint, for example. The way I read the article, though, indicates that the researchers controlled for income and perhaps also for education. If this is true, the findings can be useful.

But be careful about how much to attribute to lead. The crucial paragraphs are these:

The theory offered by the economist, Rick Nevin, is that lead poisoning accounts for much of the variation in violent crime in the United States. It offers a unifying new neurochemical theory for fluctuations in the crime rate, and it is based on studies linking children's exposure to lead with violent behavior later in their lives.

What makes Nevin's work persuasive is that he has shown an identical, decades-long association between lead poisoning and crime rates in nine countries.

"It is stunning how strong the association is," Nevin said in an interview. "Sixty-five to ninety percent or more of the substantial variation in violent crime in all these countries was explained by lead."

Note the word "variation". It is not the case that lead exposure would explain 65-90% of all crime, only in variations of that crime rate across locales and perhaps time periods. To give a rough example (with no actual basis in any real numbers), suppose that violent crime has increased by 10% over some time period in one place. Then what Nevin argues is that between 6.5 and 9 of those percentage points are attributable to greater lead exposure.

That is still quite a strong finding, if true.