Although the Supreme Court banned capital punishment for child rape, the justices have made clear that for homicide, states may inflict the ultimate penalty. To support their competing conclusions, different members of the court invoked work by Harvard law Prof. Cass Sunstein and University of Pennsylvania business Prof. Justin Wolfers on the deterrent effects of the death penalty. Unfortunately, they misread the evidence, Sunstein and Wolfers write in the Washington Post.
In states with the death penalty, the average murder rate is about 40 percent higher than in states without the death penalty. Yet such comparisons are surely confounded by other influences, as those states that impose the death penalty also have a historic culture of violence, including lynching. Te 12 states that have not executed a prisoner since 1960 comprise a useful comparison group; murder rates in these states have largely tracked those in states that subsequently adopted or rejected the death penalty. 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, says Sunstein and Wolfers. 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. Why is the Supreme Court debating deterrence? A prominent line of reasoning holds that if capital punishment fails to deter crime, it serves no useful purpose and hence is cruel and unusual, violating the Eighth Amendment.