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Capital punishment, Murder rates, States, Crime deterrence, Econometric analysis, Aggregation bias
Recent empirical studies by economists have shown, without exception, that capital punishment deters crime. Using large data sets that combine information from all fifty states over many years, the studies show that, on average, an additional execution deters many murders. The studies have received much publicity, and death penalty advocates often cite them to show that capital punishment is sound policy.
Indeed, deterrence is the central basis that many policymakers and courts cite for capital punishment. For example, President Bush believes that capital punishment deters crime and that deterrence is the only valid reason for capital punishment. Likewise, the Supreme Court, when it held in its landmark 1976 decision that capital punishment was constitutional, cited deterrence as one of its main reasons. Moreover, the Court confirmed that the main factor that motivated most state legislatures to prescribe capital punishment was deterrence. Similarly, a central issue in debates on whether federal law should include capital punishment is deterrence. We can also reasonably assume that juries and trial judges, in deciding whether to impose or overturn death sentences, will incorporate common understandings about deterrence. Governors may be similarly influenced in making decisions about clemency.
In contrast to the economic studies, recent studies by sociologists and law professors have reached an opposite conclusion. The studies are often restricted to a single state or small group of states rather than economists' examination of the average for the nation as a whole. They usually find no deterrence. Death penalty opponents cite these studies.
Each group tends to ignore the other's research. In this paper, I reconcile the results and show that both conclusions can be correct.
Using the same large data set of U.S. counties from 1977 to 1996 that many other crime studies use (and that I used in one of my earlier studies), I change the focus from national averages for deterrence. Instead, I examine whether capital punishment's impacts on murder rates differ among states.
The results are striking. Consider the twenty-seven states where at least one execution occurred during the sample period. Executions deter murder in only six states. Capital punishment, however, actually increases murder in thirteen states, more than twice as many as experience deterrence. In eight states, capital punishment has no effect on the murder rate. That is, executions have a deterrent effect in only twenty-two percent of states. In contrast, executions induce additional murders in forty-eight percent of states. In seventy- eight percent of states, executions do not deter murder.
Michigan Law Review
Joanna M. Shepherd, Deterrence versus Brutalization: Capital Punishment's Differing Impacts among States, 104 Mich. L. Rev. 203 (2005).