How the Supreme Court Misread My Research: Empirics and the Death Penalty
Cass Sunstein and I have an Op-Ed in today’s Washington Post, discussing the mis-reading of available empirical evidence in recent death penalty jurisprudence.
Some background: A recent Supreme Court ruling (Baze v. Rees) reaffirmed the constitutionality of the death penalty, and along the way, the justices revisited the empirical literature on whether the death penalty has been shown to be an effective deterrent.
Justice Stevens cited research by John Donohue and myself in concluding that “there remains no reliable statistical evidence that capital punishment in fact deters potential offenders.” Countering this, Justice Scalia cited a paper by Cass Sunstein and Adrian Vermeule, in arguing that the data do in fact point to 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.”
Our close reading of the court’s decision leads us to conclude that:
“Unfortunately, they [the Supreme Court] misread the evidence.”
To Justice Scalia, we recommend an updated reading list. Justice Scalia
relies on the suggestion by Sunstein and Vermeule that some evidence suggests a possible deterrent effect. But that suggestion actually catalyzed Donohue and Wolfers’s study of available empirical evidence. Existing studies contain significant statistical errors and slightly different approaches yield widely varying findings, a problem exacerbated by researchers’ tendency to report only those results supporting their conclusions. This led Sunstein and Vermeule to acknowledge: “We do not know whether deterrence has been shown … Nor do we conclude that the evidence of deterrence has reached some threshold of reliability that permits or requires government action.
To Justice Stevens, who suggests that “In the absence of such evidence, deterrence cannot serve as a sufficient penological justification for this uniquely severe and irrevocable punishment,” we provide a note of caution:
“the absence of evidence of deterrence should not be confused with evidence of absence.”
The morality of the death penalty is a tough question, to be sure. But it should not be further complicated by a misreading of the evidence.
For those interested in the empirical observations in our Op-Ed, I have put together a longer document discussing that evidence, available here; there are plenty of pretty pictures and pointers to background material.