Tuesday, November 27, 2012

Murder, Single Mothers and Data

So there's an article in The Atlantic today pretty much debunking the myth that a rise in children of single mothers caused the a rise in murder rates and other violent crimes around the 80's.  This same idea was famously propounded by Steven Levitt of Freakonomics fame, in which he argued the drop in crime rates in the 90's was due to more abortions of unwanted children (debuked in part here).

Now, its not only problematic that both these arguments were wrong, but that there was very good data explaining the real cause of the spike and subsequent drop in crime rates.  Look at this chart of single mothers and crime rates v time.

Now look at this chart.

You can see the crime rate and the lead usage rate are very similar in shape, just time shifted by about 20 years.  Lead usage peaks about 1975, while crime rates peak about 1993.  In other words, you can see a correlation between infant lead exposure and violent crime rates when those children reach their late teens and 20's.  Now, this could of course be coincidental.  Except you can see almost exactly the same correlation in every country which instituted lead abatement around the world (at different times), basically filtering out any other confounding factors.  See http://www.washingtonpost.com/wp-dyn/content/article/2007/07/07/AR2007070701073.html , http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0050101 and http://www.bridges4kids.org/news/10-02/Sun5-9-02.html .

The effects of lead on brain development and its links to lower IQ, antisocial behavior and impulse control are well documented and the link to criminal behavior has been known for well over 2 decades.  This makes it particularly embarrassing for Levitt, who published his abortion research in 2001.  He admits now that his statistical methods were flawed, but not that he basically ignored a much more robust data set and theory which pointed to lead as the key factor.  Though clearly Levitt has done some good work, I've found his popular writing to be driven by sensationalism, ego and money.  "Freakonomics" is a brand more than any kind of science.

But the real message here is if we want to decrease crime rates and increase academic achievement continued effort into urban lead abatement is probably one of the most effective ways.  And also, a clever narrative explanations can be very convincing and quickly become conventional wisdom accepted by all the Very Serious People while still being completely wrong.

No comments:

Post a Comment