Date: April 18, 2012
FOR IMMEDIATE RELEASE
Current Research Not Sufficient to Assess Deterrent Effect of the Death Penalty
WASHINGTON — Research to date on the effect of capital punishment on homicide rates is not useful in determining whether the death penalty increases, decreases, or has no effect on these rates, says a new report from the National Research Council. The committee that wrote the report evaluated studies conducted since a four-year moratorium on the death penalty was lifted in 1976, and it found that the studies do not provide evidence for or against the proposition that the death penalty affects homicide rates. These studies should not be used to inform judgments about the effect of the death penalty on homicide, and should not serve as a basis for policy decisions about capital punishment, the committee said.
The lack of evidence about the deterrent effect of capital punishment -- whether it is positive, negative, or zero -- should not be construed as favoring one argument over another, the report stresses. "Fundamental flaws in the research we reviewed make it of no use in answering the question of whether the death penalty affects homicide rates," said Daniel S. Nagin, Teresa and H. John Heinz III University Professor of Public Policy and Statistics at Carnegie Mellon University Pittsburgh, and chair of the committee that wrote the report. "We recognize that this conclusion may be controversial to some, but no one is well-served by unsupportable claims about the effect of the death penalty, regardless of whether the claim is that the death penalty deters homicides, has no effect on homicide rates or actually increases homicides."
The key question, the report says, is whether capital punishment is less or more effective as a deterrent than alternative punishments, such as a life sentence without the possibility of parole. Yet none of the research that has been done accounted for the possible effect of noncapital punishments on homicide rates.
The committee also found that studies made implausible or unsupported assumptions about potential murderers' perceptions of and response to capital punishment. Many studies did not address how perceptions are formed and simply inferred that potential murderers respond to the objective risk of execution. This inference ignores the fact that determining the objective risk poses great complexities even for a well-informed researcher, let alone a potential murderer. For instance, only 15 percent of people who have been sentenced to death since 1976 have actually been executed, and a large fraction of death sentences are reversed. Furthermore, estimates of the deterrent effect of the death penalty were based on unfounded assumptions, for example, that the effect of capital punishment is the same across all the states and over time. There is no evidence to support such suppositions.
These intrinsic shortcomings severely limit what can be learned from the existing research, the report says. The committee recommended next steps for research that include collecting data that consider both capital and noncapital punishments for murder, conducting studies on how potential murderers perceive a range of punishments in homicide cases, and using statistical methods based on more credible assumptions about the effect of capital punishment on homicide rates.
The ultimate success of the research may depend on the specific questions being addressed, the report adds. Questions of interest include if and how the legal status or intensity of use of the death penalty affects homicide rates or whether executions affect these rates in the short term. The report acknowledged that new data and knowledge may not come quickly or easily, but such research may help to provide insight into the crime prevention effects of noncapital punishment that could be useful for future policy decisions.
The committee was not asked and did not investigate the moral arguments for or against capital punishment, the empirical evidence on whether capital punishment is administered in a nondiscriminatory and consistent fashion, or the cost of its administration.
The study was sponsored by Tides Foundation, the Proteus Action League, and the National Institute of Justice. The National Academy of Sciences, National Academy of Engineering,
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NATIONAL RESEARCH COUNCIL
Division of Behavioral and Social Sciences and Education
Committee on Deterrence and the Death Penalty
Daniel S. Nagin (chair)
Teresa and H. John Heinz III University Professor
of Public Policy and Statistics
Edwin A. and Betty L. Bergman Distinguished
Phillip J. Cook1
Steven N. Durlauf
Kenneth J. Arrow and Laurents R. Christensen Professor of Economics
Amelia M. Haviland
Gerard E. Lynch
United States Circuit Judge
Charles F. Manski2
Board of Trustees Professor in Economics
Department of Economics
James Q. Wilson