Police effects

Geoff Simmons makes some good points about overreliance on prisons, but I think he's got this part wrong:

The Labour/NZ First answer of more police is also no real solution either. More police means more people in prison and we know more people in prison just leads to more crime.

Empirical work on police numbers and crime is hard because of obvious endogeneity issues: police hiring is also a response to crime rates.

But the best approach I've seen to the problem finds an elasticity of crime with respect to police numbers of -0.3. A ten percent increase in the number of police reduces the crime rate by 3 percent in US work. If we figure that police have diminishing marginal effects at the relevant margins, and that our policing intensity is lower than America's, then effects here would be stronger. I'd done some back-of-the-envelope reckons on this a while back suggesting that police hiring could be rather cost effective. Increasing the probability of being caught can be pretty strong deterrent.