Death penalty deterrence: No good evidence

Did you know that many scholars still believe the death penalty deters crime? I didn't.

Among others, Richard Posner, an influential appeals court judge and legal scholar, and Nobel laureate Gary Becker have both recently endorsed scholarship suggesting that the death penalty deters homicide.

But a very useful article by John Donohue and Justin Wolfers in The Economist's Voice demolishes that claim (registration required to view PDF). Reanalyzing the most prominent recent paper in the field, which claims to find that each execution deters 18 homicides, they find that standard econometric adjustments for the structure of the data yield a confidence interval ranging from "119 lives saved per execution to 82 lives lost" -- essentially, a null result. (And there are a number of other, more technical problems with the paper in question -- see also this followup.) Donohue and Wolfers then reanalyze a superior dataset and find that most model specifications suggest an increase in executions is associated with a limited increase in the number of homicides.

In short, there does not appear to be any convincing empirical evidence that the death penalty deters homicides. Some may support the death penalty for moral reasons alone, but for most Americans, that is not enough. I suspect that the combination of this finding and the threat of executing innocent people will cause more states to roll the policy back in the future.

Update 7/18 10:46 AM: Here's the Stanford Law Review paper on which the Donohue and Wolfers article referenced above is based (registration required to view PDF).

Comments

[David B.]

Do you have any evidence of your assertion that most Americans do not support the death penalty for moral reasons alone? Also, what would those moral reasons be?

I have always read and heard that most Americans support the death penalty. If that is the case, then a significant portion of those would have to support the death penalty for other reasons, such as a deterrent factor. Has a polling been done on that question - i.e. "Would you support the death penalty if it did not have any deterrent effect?"

[Kit Burns]

I don't think that the death penalty is a deterrent. People who are considering murder are always sure they won't get caught "as they are too clever". Look at how many murders occur in the US annually. If someone is out for murder, not much will stop them. My concern is that life in prison does not mean life in prison. Why is Manson and Sirhan Sirhan up for parole?

[pcomeau]

Kit Burn:
In the case of Manson and Sirhan... I believe they are up for parole due to the fact that at the time of conviction there was no such thing as life w/out parole in the state law. It is my understanding (though I could be wrong) that the law was changed after they were convicted. But... they are grandfathered in, so hence the parole option.

In other words this is a technicality of state law and really mute in the overall argument of life in prison vs. death penalty.

In addtion most states w/ the death penalty have a law that requires the case to be appealed. So the defendent ends up in a multi year process that can cost as much and sometimes more than if they had simply been sentenced to life w/o parole.

David B:
On the front of American supporting or not supporting the death penalty depends on how the question is asked. It's not a simple yes/no. Most Americans (in my opinion) support it either on grounds of prevention and/or abilty to contain the violence. In other words remove the killer so he can't kill again, and it will serve as a lesson to others. The problem is that neither really works. Most murders are acts of passion (serial killers are rare) and because of that, a death penalty doesn't really prevent future murders. (again my opion based on various readings of the topic.)