1. Does the available evidence provide a reasonable basis for drawing conclusions about the magnitude of capital punishment’s effect on homicide rates?
2. Are there differences among the extant analyses that provide a basis for resolving the differences in findings? Are the differences in findings due to inherent limitations in the data? Are there existing statistical methods and/or theoretical perspectives that have yet to be applied that can better address the deterrence question? Are the limitations of existing evidence reflective of a lack of information about the social, economic, and political underpinnings of homicide rates and/or the administration of capital punishment that first must be resolved before the deterrent effect of capital punishment can be determined?
3. Do potential remedies to shortcomings in the evidence on the deterrent effect of capital punishment have broader applicability for research on the deterrent effect of noncapital sanctions?
CONCLUSION AND RECOMMENDATION: The committee concludes that research to date on the effect of capital punishment on homicide is not informative about whether capital punishment decreases, increases, or has no effect on homicide rates. Therefore, the committee recommends that these studies not be used to inform deliberations requiring judgments about the effect of the death penalty on homicide. Consequently, claims that research demonstrates that capital punishment decreases or increases the homicide rate by a specified amount or has no effect on the homicide rate should not influence policy judgments about capital punishment.
The committee was disappointed to reach the conclusion that research conducted in the 30 years since the earlier NRC report has not sufficiently advanced knowledge to allow a conclusion, however qualified, about the effect of the death penalty on homicide rates. Yet this is our conclusion. Some studies play the useful role, either intentionally or not, of demonstrating the fragility of claims to have or not to have found deterrent effects. However, even these studies suffer from two intrinsic shortcomings that severely limit what can be learned from them about the effect of the death penalty—as it has actually been administered in the United States in the past 35 years—on the death penalty.
Properly understood, the relevant question about the deterrent effect of capital punishment is the differential or marginal deterrent effect of execution over the deterrent effect of other available or commonly used penalties, specifically, a lengthy prison sentence or one of life without the possibility of