The Murky Evidence For and Against the Death Penalty as Deterrence
The Supreme Court looked at death penalty as deterrent arguments before ruling to reaffirm its constitutionality in Baze v. Rees this term. The opinion [pdf] cited research by both Cass R. Sunstein (arguing that the data points to deterrence) and Justin Wolfers (no deterrence).
As two of the supposed flag bearers for the competing views cited by the court, Sunstein and I thought it worth poring over the data to see what we agree on. It turns out there’s a lot of agreement between us:
“In short, the best reading of the accumulated data is that they do not establish a deterrent effect of the death penalty.”
Wolfers and Sunstein have an OpEd in the WaPo today titled A Death Penalty Puzzle:
To support their competing conclusions on the legal issue, different members of the court invoked work by each of us on the deterrent effects of the death penalty. Unfortunately, they misread the evidence.
Justice John Paul Stevens cited recent research by Wolfers (with co-author John Donohue) to justify the claim that “there remains no reliable statistical evidence that capital punishment in fact deters potential offenders.” Justice Antonin Scalia cited a suggestion by Sunstein (with co-author Adrian Vermeule) that “a significant body of recent evidence” shows “that capital punishment may well have a deterrent effect, possibly a quite powerful one.”
What does the evidence actually say?
After a very interesting review their conclusion is… inconclusive:
The number of homicides is so large, and varies so much year to year, that it is impossible to disentangle the effects of execution policy from other changes affecting murder rates. Moreover, execution policy doesn’t change often or much. Just as a laboratory scientist with too few experimental subjects cannot draw strong conclusions, the best we can say is that homicide rates are not closely associated with capital punishment. On the basis of existing evidence, it is especially hard to justify claims about causality.
Justice Stevens argues, “In the absence of such evidence, deterrence cannot serve as a sufficient penological justification for this uniquely severe and irrevocable punishment.” Perhaps. But the absence of evidence of deterrence should not be confused with evidence of absence.
Why are we talking deterrence anyway?
A prominent line of reasoning, endorsed by several justices, holds that if capital punishment fails to deter crime, it serves no useful purpose and hence is cruel and unusual, violating the Eighth Amendment. This reasoning tracks public debate as well. While some favor the death penalty on retributive grounds, many others (including President Bush) argue that the only sound reason for capital punishment is to deter murder.
We concur with Scalia that if a strong deterrent effect could be demonstrated, a plausible argument could be made on behalf of executions. But what if the evidence is inconclusive?
We are not sure how to answer that question. But as executions resume, the debates over the death penalty should not be distorted by a misunderstanding of what the evidence actually shows.
For more, Wolfers’ Freakonomics blog post has a wealth of rich links. Check it out!