theory (Kahneman and Tversky, 1979) predicts that low probability events, such as execution, are either overweighted compared to models based on objective probabilities or not considered at all. While each of these perspectives on the deterrence process shares a common view that criminal decision making involves a balancing of costs and benefits, the conceptualization of how this balancing occurs varies greatly across theories. Most importantly for our purposes, the different models are based on different conceptions of how sanction risks are perceived and affect behavior.

A less studied dimension of the classical formulation of deterrence is the concept of celerity—the speed with which a sanction is imposed. In the case of the death penalty, celerity may be a particularly important dimension of the classical formulation. According to the Bureau of Justice Statistics (2010), the average time to execution for the executions that occurred between 1984 and 2009 was 10 years. This statistic, however, pertains only to the small minority of persons sentenced to death who have actually been executed. Only 15 percent of death sentences imposed since 1976 have been carried out. Thus, some individuals have been on death row for decades and indeed may die by other causes before they can be executed. Indeed, according to the Bureau of Justice Statistics (2010, Table 11) there have already been 416 such deaths (1973-2009) among death row inmates. For these offenders, their sentence was, in fact, equivalent to a life sentence.

The studies we review do little to reveal the underlying mechanisms that generate the associations that are estimated between the death penalty and the homicide rate. Indeed, it is possible that these associations reflect social processes that are distinct from deterrence in the narrow sense discussed above. For example, Andenæs (1974) and Packer (1968) speculate that independent of the sanctions prescribed in the criminal laws, the laws themselves may reduce the incidence of the prohibited acts by moral education and related social processes. Thus, providing the legal authority for the use of the death penalty for a special class of murders might prevent murders of that type by making clear that these types of murder are deemed particularly heinous. Alternatively, the brutalization hypothesis predicts the opposite effect.

Given these possible and unknown underlying mechanisms, in the remainder of this report we discuss empirical estimates of the effects of the death on the homicide rate, not “deterrent” effects. Even more important than this point of nomenclature are the implications of alternative possible mechanisms for using empirical findings on the death penalty effects to predict effects on the crime rate of alternative sanction regimes. As we discuss below, alternative mechanisms can imply very different inferences and interpretations. We emphasize this point because the issue of mechanisms is one of several reasons that inferences about the causal effect of capital punishment on homicide rates cannot be reduced to a simple statistical exercise:

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