Thursday, April 17, 2008

Marginal Deterrence and Child Rape

Slate's always excellent Dahlia Lithwick has a good summary of the recent Supreme Court cases regarding capital punishment. One of the cases is regarding whether or not discomfort or pain during lethal injection (or any execution method) makes it cruel and unusual; the court announced its decision (the court supported lethal injection 7 to 2). The other case is regarding whether or not rapists can be executed for the rape of children; the court heard arguments on this yesterday. It is the latter of these two that interests me.

Let's go ahead and get this over with first, just to be sure that no one accuses me of being a fan of rapists or child rapists: rape is a horrible evil, and the rape of a child is even more horrible than the rape of an adult. Clearly rapists should be severely punished.

The question is, what should that punishment be? Should it be death? Rape seems such a horrible crime that death does not seem unreasonable. Yet there is an important reason to believe that capital punishment for rapists would be a bad idea, not for the sake of the rapists, but for the sake of their victims.

The problem is what economists call marginal deterrence. If the punishment for rape is execution, and if that is the same as the punishment for murder, then the marginal cost of committing murder after committing rape is zero. That is, punishing rapists with death gives them an incentive to kill witnesses, particularly their victim. The result of execution of rapists may be slightly fewer rapes, but possibly a significantly higher number of the remaining rapes may end up with dead victims. I am personally uncomfortable with the idea of reducing rapes at the cost of additional murders, particularly if these victims are children.

When deciding the punishments for crimes, the absolute punishment is not the only thing that matters. The relative punishment for different crimes also matters. Unfortunately there was no discussion (from what I have read, anyway) of this at all in the Supreme Court. My low opinion of the court remains unchanged.

I anticipate three possible responses to this argument (there are surely more):
  • Marginal deterrence could still be preserved if rape + murder results in a higher probability of execution than rape alone, resulting in higher expected punishment.
The problem with this argument is that I can't really imagine many circumstances in which one could claim mitigating factors in raping a child, resulting in a lesser sentence. Furthermore, any factors that might matter--insanity, for example--might also reduce the probability of murder conviction. It is hard for me to imagine someone wriggling out of the death penalty for the rape of a child, but then being convicted for the murder of that child. If this really did happen, it would suggest that the death penalty for rape doesn't really have teeth.

  • Punishment isn't about deterrence at all.
I don't think that anyone is really this indifferent to the effects of poor punishment design, are they? Wouldn't someone interested in justice care if the result of this change was more dead children?

  • Changes in punishment do not affect the behavior of criminals, i.e., deterrence doesn't work.
The usual argument behind this claim is that criminals are irrational and do not respond to incentives. I think there is evidence to counter this claim, although I do not have time to summarize the entire literature here. More importantly, I think that most people really know that this argument is false, as a result of simple everyday experience. Why do parents discipline their children? Because children tend to respond. Yes, different children respond to different degrees, but a response is usually expected, and it usually occurs. If punishment does not affect behavior, why do we have laws and regulations that impose monetary punishments? Imprisonment at least makes sense on the grounds that the criminal is removed from the population, and unable to commit additional crimes. Fines and fees and similar punishments only make sense if we believe that people will respond by altering their behavior. Why should criminals--particularly the cold, calculating sort--be any different?