During the recent UK riots, it became apparent that most pundits had forgotten their Freakonomics. I reproduce a piece of their wisdom here. It applies to the US, of course, but still....
We spent an entire chapter in Freakonomics exploring the factors that do and do not seem to have brought down the rate of violent crime in the U.S. In short, factors that matter include: number of police; number of prisoners; changes in drug markets; and the availability of abortion. And those that don’t seem to much matter: the economy; innovative policing strategies; most gun laws; capital punishment; and demographics.
For the full link, see