Freakonomics on crime

March 25, 2009

I read the book “Freaknomics” recently and enjoyed it, mostly, although in the end it turned out to be a disappointment. In the introduction is said something like “economics is a set of tools that allows us to study incentives and how people respond to them” but really the only tools I saw being used were a) plain old statistics and b) plain old conjecture.

One of the chapters  I enjoyed most at first was the one on abortion and crime – the authors attribute the fall in violent crime in the 90s in the US to the legalisation of abortion around 20 years previously. Fewer unwanted kids = fewer criminals, they say. At first I went “oh yeah, that makes sense” and, on the surface, it does, and they use a lot of science-y sounding language to back up their case which would be inclined to convince a fella.

But then at the back of the book they answer some detractors who’ve found fault with their approach by giving some more technical information on the statistical analysis they’ve used. They modify their treatment of the data saying the new way is “more accurate”, and end up with a stronger relation between abortions 20 years ago and the crime drop today. I don’t really have the statistical chops to check whether their analysis is reasonable, but this carry-on makes me suspicious – is their new treatment really more accurate, or are they just massaging the data so that it agrees with their thesis better?

I’m not sure I trust these guys. They attribute the rise in crime in the US during the 1960s to the (for the US) “liberal” political regime that was in place at the time and not to the big upsurge in drug use, but say the rise in crime during the 80s when there was a right-wing regime in power was exclusively due to drugs (crack cocaine in particular). Hmmm.

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