Long-chain correlation: lead paint and crime

ChrisHibbert

A friend has been asking my views on the likelihood that there's anything to a correlation between changing levels of lead in paint (and automotive exhaust) and the levels of crime. He quoted from a Reason Blog:

So Nevin dove in further, digging up detailed data on lead emissions and crime rates to see if the similarity of the curves was as good as it seemed. It turned out to be even better: In a 2000 paper (PDF) 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.

I responded with the following:

Sounds like a stretch to me. I'd want to hear that they didn't test more than 5 other hypothesis before coming to that conclusion, or the p value was far better than .05. I kind of doubt that either is the case.

He's apparently continued to pursue the question, and just forwarded these remarks from Steven Pinker that I thought were very illuminating, and probably deserve a place in this community's toolkit for skeptics. Pinker's main point is that the association between Lead and crime is a long tenuous chain of suppositions, and several of the intermediate points should be far easier to measure. Finding correlations at this distance is not very informative.

http://stevenpinker.com/files/pinker/files/pinker_comments_on_lead_removal_and_declining_crime.pdf

Does the phrase "long-chain correlation" stick in your head and make it easier to dismiss this kind of argument?

So Nevin dove in further, digging up detailed data on lead emissions and crime rates to see if the similarity of the curves was as good as it seemed. It turned out to be even better: In a 2000 paper (PDF) 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.

I responded with the following:

Sounds like a stretch to me. I'd want to hear that they didn't test more than 5 other hypothesis before coming to that conclusion, or the p value was far better than .05. I kind of doubt that either is the case.

http://stevenpinker.com/files/pinker/files/pinker_comments_on_lead_removal_and_declining_crime.pdf

Does the phrase "long-chain correlation" stick in your head and make it easier to dismiss this kind of argument?

The lead/crime theory seems to have entered blogospheric conversation-space thanks to an article by Mother Jones writer/blogger Kevin Drum. Here's a link to most of what he's written on the subject in the past month. Here's an excerpt from the short version/intro to the magazine article:

The chart [above] illustrates the basic data that inspired the lead hypothesis: it shows lead emissions starting in 1935 overlaid with the violent crime rate 23 years later. The two curves match almost perfectly.

Now, I know my readers, and first thing a lot of you are going to do is yell at me: "Correlation is not causation!" And that's true. If this curve were the only bit of evidence we had, the connection between lead and violent crime would be pretty thin. But it's not. You should read the story to understand just how many different studies confirm this relationship...

We now have a huge amount of evidence linking lead to violent crime. We have evidence not just at the national level, but also at the state level, the city level, and the international level. We have longitudinal studies that track children from birth to adulthood to find out if higher blood lead levels lead to more arrests for violent crimes. And perhaps most important, this is a theory that just makes sense. Everything we now know about the effects of lead on the brain tells us that even moderately high levels of lead exposure are associated with aggressivity, impulsivity, ADHD, and lower IQ. And right there, you've practically defined the profile of a violent young offender.

Your first MotherJones link seems a bit inaccurate... Try this one

I was about to post on this subject myself to see if there were any LessWrong opinions. It's certainly more than just one US-wide correlation; similar correlations appear at the level of individual states and cities, and internationally too. Plus there are longitudinal studies (following cohorts of children with different measured lead exposures through time, and monitoring levels of school delinquency then criminality).