Wednesday 28 September 2011

Death penalty

I used to hold the position that the death penalty was wrong, despite that it likely deterred around eight murders per execution, on the basis that the State ought not have that right. I suppose if the likely deterrent effect were really large, I'd be pluralist enough for the utilitarian side to beat the libertarian side. But not at that deterrent rate.

Wolfers and Donohue had previously shown much of the empirics on the death penalty are fragile.

The latest from Manski and Pepper (HT: Chris Blattman) shows the results more fragile than I'd thought: you can pretty much choose your conclusion through appropriate choice of identifying assumptions.
...we study the identifying power of relatively weak assumptions restricting variation in treatment response across places and time.  The results are findings of partial identification that bound the deterrent effect of capital punishment.  By successively adding stronger identifying assumptions, we seek to make transparent how assumptions shape inference.  We perform empirical analysis using state-level data in the United States in 1975 and 1977.  Under the weakest restrictions, there is substantial ambiguity: we cannot rule out the possibility that having a death penalty statute substantially increases or decreases homicide.  This ambiguity is reduced when we impose stronger assumptions, but inferences are sensitive to the maintained restrictions.  Combining the data with some assumptions implies that the death penalty increases homicide, but other assumptions imply that the death penalty deters it.
And so I revise: the death penalty is wrong, and it also likely has little measurable deterrent effect. There may still be a deterrent effect; we just can't show one given available data.

Update: Chris Auld has a nice intuitive explanation of the paper's results.


  1. I'm no fan of the death penalty for one really good reason - sometimes innocent people get arrested, tried and convicted. It is bad enough that an innocent might spend several years in prison, worse still that the state should kill that person. The death of even one innocent is one too many.

  2. I think that the Singaporean experience demonstrates that there is a deterrent effect associated with the death penalty.  I am inclined to accept Levitt's view that, in the US case, the very low probability of receiving the death penalty and the length of time spent on death row negate any deterrent above and beyond that of prison.  It would be possible to reduce murder rates below current levels, in either New Zealand or the US, using the death penalty.  But, to do so, a very high proportion of those convicted of murder would need to be executed and this would necessitate removing many of the safeguards that exist in the US system to drastically shorten the time between the commission of the crime and the execution.  This would make executions cheaper, but it would no doubt mean that an appalling number of people were executed for crimes they didn't commit. 
    I think that this is my major problem with the death penalty.  To make it useful, it must be horrifically draconian, and to ensure that only those who were guilty beyond all doubt were executed it must necessarily be extremely expensive and serve no purpose beyond satiating a sanguinary desire for vengeance. 
    I don't think I agree that the state doesn't have the right, though.  If someone were to murder a member of my family, I believe I have a prima facie right to enact vengeance in kind.  However, in a civilised society, my right to vengeance is effectively delegated to the state.  It is incumbent upon the state to exercise that right justly.  I believe it is possible for the death penalty to be used justly, but as above, I don't think that doing so is worthwhile or desirable.

  3. The death penalty used to be applied more frequently and swiftly for murder in the U.S (even before Mark Kleiman had written his book!). Steve Dutch argues that the legal changes which have reduced the rate of executions have actually made the system less fair:

  4. @Lats: I'm even squeamish about killing guilty people.

    @NZClassicalLiberal: I'd flip that a bit: I would be more comfortable with the death penalty if, assuming for now a system that only convicts the guilty, the person who would have been justified in exacting vengeance in a private system be the one who gets to do it. After having talked with the family and friends of the person he was to kill. And after having dined with the person he was to kill. And having to look the person in the eye while killing him. And having the option at any point to commute the sentence.

    @Wonks: I'd believe it.

  5. I can see the merit in such a system, but I don't think it's just that one's sentence should be dependent upon the mood of the person one offends against, or that person's family. This is one of the reasons that the right to vengeance is best delegated.

  6. I agree that the very low probability of receiving the death penalty and the protracted death row stay do negate the deterrent value. The consequences for committing crimes have been watered down past the point where they matter.

    But I also wonder if we've made executions too sterile with lethal injections. Perhaps the more graphic penalties (like hanging or electrocution) held greater deterrent bang for the buck. Maybe by making deaths more humane, we've negated much of the fear of it too.

    It's unimaginable that we're agreeable with letting these scumbags living out their lives in relative security and comfort on our tax dollars. Instead I think it's more a case of apathy - the citizens know that there's little they can do to cause the broken justice system to be reformed, so they've grown numb to it all. Why fret and worry over something you cannot fix?

  7. Rob: check my post on flogging. I worry that by making incarceration seem too humane, we come to rely on it too much.