Does the death penalty work?

Cover Deterrence and the Death PenaltyA committee of the National Research Council has completed a review of the evidence on the deterrent value of the death penalty and concluded that current studies do not provide much evidence that the death penalty affects homicide rates.

You can read the press release summarizing the findings or take a look at the full report online.

The committee’s conclusions (from the full report):

The committee concludes that research to date on the effect of capital punishment on homicide is not informative about whether capital punishment decreases, increases, or has no effect on homicide rates. Therefore, the committee recommends that these studies not be used to inform deliberations requiring judgments about the effect of the death penalty on homicide. Consequently, claims that research demonstrates that capital punishment decreases or increases the homicide rate by a specified amount or has no effect on the homicide rate should not influence policy judgments about capital punishment.

Those findings are not going to excite a lot of people. As the committee points out, the existing research has produced conflicting results and the debate has often spawned more political fighting than informed debate.

The study will probably produce two interesting responses:

Why [use the death penalty]?

Some people will ask why we utilize such a drastic and irreversible form of punishment when we are not sure of its impact.

Why not [use the death penalty]?

Others will ask why worry about the deterrent value of the death penalty since it can serve justice in other ways and the society has the right to retribution.


So… what’s wrong with the existing studies?

The report cites two problems with the existing research on the death penalty:

(1) It does not look at the “differential deterrent effect of execution in comparison with the deterrent effect of other  available or commonly used penalties.” That is, does the prospect of being executed discourage potential criminals beyond other possible punishments dished out in the state? We don’t know if crime is deterred by the existence of capital punishment or the kind of generally tough-on-crime mentality that will manifest itself in punishment other than the death penalty.

(2) We don’t know how criminals think about the death penalty or how they weigh such punishment in their decision to commit a crime. Most of us generally assume that the government promising to kill killers makes society’s intentions pretty clear. However, I have to admit that I know nothing of the state of mind behind a murder and projecting my rationality onto someone who is doing something I consider unimaginable is silly.

The problem of looking at how potential murders assess risk is complicated by the fact that only 15% of people sentenced to death have actually been executed. That means that a death sentence isn’t always a death sentence. Knowing that the state might not follow through on the intention to execute people may undermine the deterrent value of capital punishment. To compute the odds that they will be executed potential murder would have to calculate the probability that they would get caught/convicted/sentenced and then multiply that by the likelihood that the state will follow through on an execution.

Unfortunately, this study seems to pretty accurately reflect our real understanding of the death penalty and left with more uncertainty about its impact than we’re comfortable with.


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