Rational, forward looking criminals

This Slate piece argues that prison does not deter crime (although locking up offenders does prevent them from engaging in more crime).

...the probability of being sentenced to prison for an offense jumped from 3 percent to 17 percent at exactly age 18. This tees up the answer to the economists' main question: How does the tendency to commit crimes vary around the 18th birthday, when the odds of a prison-sentence punishment jump? The answer is, hardly at all. While the probability of being arrested each week falls steadily from age 17 to age 19, there is no sizeable decrease in the arrest rate that corresponds to the bump up to an adult penalty in the weeks before and after people turn 18. To an economist, this is odd. At the grocery store, in weeks that Coke is on sale and Pepsi is not, consumers respond immediately. Coke sells out while Pepsi languishes on the shelf.

The rational, forward looking utility maximizing criminal would consider 1) how likely they are to be arrested, 2) how likely they are to be sentenced if they are arrested, and 3) the likely severity of the sentence they will receive (if they get one at all), when deciding how much crime to commit. All else equal, you might expect a little crime spurt just before the 18th birthday, and then a lower level of crime after that.

There are good reasons why young criminals may deviate more from the model rational utility maximizer than most -- they may have very short time horizons. So the increase in the severity of sentence (time they will spend in prison) does not matter much to them. They may respond more to a greater likelihood of getting caught or sentenced, or failing that, a punishment that increases in severity through immediate unpleasantness, not increased duration, like public flogging.