I’m not a toxicologist, a criminologist or a statistician (and I’d be interested to hear from anyone with expertise in these fields). But I think Kevin Drum at Mother Jones makes a compelling case for a causal relationship between the rise and fall of violent crime rates in the US and other countries and the rise and fall (especially since the elimination of leaded gasoline) in the amount of lead in the environment.
Although I hope people will read Drum’s entire piece before commenting, I’ll note one passage in particular:
[A] single correlation between two curves isn’t all that impressive, econometrically speaking. Sales of vinyl LPs rose in the postwar period too, and then declined in the ’80s and ’90s. Lots of things follow a pattern like that. So no matter how good the fit, if you only have a single correlation it might just be a coincidence. You need to do something more to establish causality.
In a followup piece, Drum acknowledges that there are other possible causes for the drop in violent crime.
It’s true that one researcher has suggested that lead can explain 90 percent of the rise and fall of crime, but that’s very much the high end of the estimates in the field. I’m a lot more comfortable with an estimate of around 50 percent, something I should have made clearer in the text of my piece. In other words, lead probably explains a very big chunk of the rise and fall of postwar crime in America, but it doesn’t trump everything else. Drugs, poverty, urban gang warfare, education, policing tactics, and other things also play a role.
Drum links to a study showing a link between levels of lead in the blood of preschool children and subsequent crime rates not only in the US, but in Britain, Canada, France, Australia, Finland, Italy, West Germany, and New Zealand.