Carnegie Mellon University
April 19, 2012

News Brief: Current Research Insufficient to Assess Deterrent Effect of Death Penalty, Report Finds

Carnegie Mellon Professor Heads Report Committee, Cites Research Flaws

Contact: Ken Walters / 412-268-1051 /

Current research 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 a National Research Council committee headed by Carnegie Mellon Professor Daniel S. Nagin.

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.

"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 Nagin, the Teresa and H. John Heinz III University Professor of Public Policy and Statistics at CMU. "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. In addition, 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.