Daniel S. Nagin, PhD, Professor of Public Policy and Statistics at Carnegie Mellon University, and John V. Pepper, PhD, Professor of Economics at the University of Virginia, wrote in their 2012 book Deterrence and the Death Penalty:
"...[R]esearch to date of the effect of capital punishment on crime is not informative about whether capital punishment decreases, increases, or has no effect on crime rates. Therefore, the committee recommends that these studies not be used to inform deliberations requiring judgments about the effect of the death penalty on crime rates. Consequently, claims that research demonstrates that capital punishment decreases or increases the crime rate by a specified amount or has no effect on the crime rate should not influence policy judgments about capital punishment."
Michael Summers, PhD, MBA, Professor of Management Science at Pepperdine University, wrote in his Nov. 2, 2007 article "Capital Punishment Works" in the Wall Street Journal:
"...[O]ur recent research shows that each execution carried out is correlated with about 74 fewer murders the following year... The study examined the relationship between the number of executions and the number of murders in the U.S. for the 26-year period from 1979 to 2004, using data from publicly available FBI sources... There seems to be an obvious negative correlation in that when executions increase, murders decrease, and when executions decrease, murders increase...
In the early 1980s, the return of the death penalty was associated with a drop in the number of murders. In the mid-to-late 1980s, when the number of executions stabilized at about 20 per year, the number of murders increased. Throughout the 1990s, our society increased the number of executions, and the number of murders plummeted. Since 2001, there has been a decline in executions and an increase in murders.
It is possible that this correlated relationship could be mere coincidence, so we did a regression analysis on the 26-year relationship. The association was significant at the .00005 level, which meant the odds against the pattern being simply a random happening are about 18,000 to one. Further analysis revealed that each execution seems to be associated with 71 fewer murders in the year the execution took place...
We know that, for whatever reason, there is a simple but dramatic relationship between the number of executions carried out and a corresponding reduction in the number of murders..."
Paul H. Rubin, PhD, Professor of Economics at Emory University, wrote in his Feb. 1, 2006 testimony "Statistical Evidence on Capital Punishment and the Deterrence of Homicide” before the US Senate Judiciary Committee on the Constitution, Civil Rights, and Property Rights, available at judiciary.senate.gov:
"Recent research on the relationship between capital punishment and homicide has created a consensus among most economists who have studied the issue that capital punishment deters murder. Early studies from the 1970s and 1980s reached conflicting results. However, recent studies have exploited better data and more sophisticated statistical techniques. The modern refereed studies have consistently shown that capital punishment has a strong deterrent effect, with each execution deterring between 3 and 18 murders...
The literature is easy to summarize: almost all modern studies and all the refereed studies find a significant deterrent effect of capital punishment. Only one study questions these results. To an economist, this is not surprising: we expect criminals and potential criminals to respond to sanctions, and execution is the most severe sanction available..."
Hashem Dezhbakhsh, PhD, Professor of Economics at Emory University, and Joanna Shepherd, PhD, Associate Professor of Law at Emory University, wrote in their July 2003 study "The Deterrent Effect of Capital Punishment: Evidence from a 'Judicial Experiment'" in Economic Inquiry:
"[There is] strong evidence for the deterrent effect of capital punishment... Each execution results, on average, in eighteen fewer murders with a margin of error of plus or minus ten. Tests show that results are not driven by tougher sentencing laws and are robust to many alternative specifications...
The results are boldly clear: executions deter murders and murder rates increase substantially during moratoriums. The results are consistent across before-and-after comparisons and regressions regardless of the data's aggregation level, the time period, or the specific variable used to measure executions... [E]xecutions provide a large benefit to society by deterring murders..."
H. Naci Mocan, PhD, Professor and Chair of Economics at Louisiana State University, wrote in his 2003 study "Getting Off Death Row: Commuted Sentences and the Deterrent Effect of Capital Punishment" in the Journal of Law and Economics:
"Controlling for a variety of state characteristics, we investigate the impact of the execution, commutation, and removal rates, homicide arrest rate, sentencing rate, imprisonment rate, and prison death rate on the rate of homicide. The models are estimated in a number of different forms, controlling for state fixed effects, common time trends, and state-specific time trends. We find a significant relationship among the execution, removal, and commutation rates and the rate of homicide. Each additional execution decreases homicides by about five, and each additional commutation increases homicides by the same amount, while one additional removal from death row generates one additional homicide."
Cass R. Sunstein, PhD, Professor of Law at the University of Chicago, wrote in his Mar. 2005 paper "Is Capital Punishment Morally Required? The Relevance of Life-Life Tradeoffs” on papers.ssrn.com:
"…[C]apital punishment may be morally required not for retributive reasons, but in order to prevent the taking of innocent lives...
The foundation for our argument is a large and growing body of evidence that capital punishment may well have a deterrent effect, possibly a quite powerful one. A leading study [The Deterrent Effect of Capital Punishment: Evidence from a 'Judicial Experiment,' Hashem Dezhbakhsh and Joanna Shepherd, July 2003] suggests that each execution prevents some eighteen murders, on average... If the current evidence is even roughly correct, then a refusal to impose capital punishment will effectively condemn numerous innocent people to death...
Contrary to widely-held beliefs, based on partial information or older studies, a wave of recent evidence suggests the possibility that capital punishment saves lives...
Capital punishment may well have strong deterrent effects; there is evidence that few categories of murders are inherently un-deterrable, even so-called crimes of passion; some studies find extremely large deterrent effects; error and arbitrariness undoubtedly occur, but the evidence of deterrence suggests that prospective murderers are receiving a clear signal."
George W. Bush, MBA, 43rd President of the United States, in an Oct. 17, 2000 debate with Al Gore at Washington University, said in response to the question "Do both of you believe that the death penalty actually deters crime?":
"I do, that’s the only reason to be for it. I don’t think you should support the death penalty to seek revenge. I don’t think that’s right. I think the reason to support the death penalty is because it saves other people’s lives."
George E. Pataki, JD, 53rd Governor of New York State, in an Aug. 30, 1996 press release titled "Statement on Anniversary of Death Penalty by Governor Pataki," stated:
"New Yorkers live in safer communities today because we are finally creating a climate that protects our citizens and causes criminals to fear arrest, prosecution and punishment. ...This has occurred in part because of the strong signal that the death penalty sent to violent criminals and murderers: we won't excuse criminals, we will punish them...
I sponsored the death penalty laws because of my firm conviction that it would act as a significant deterrent and provide a true measure of justice to murder victims and their loved ones... I have every confidence that it will continue to deter murders, will continue to enhance public safety and will be enforced fairly and justly."
Ernest Van Den Haag, PhD, late Professor of Jurisprudence at Fordham University, in an Oct. 17, 1983 New York Times Op-Ed article titled "For the Death Penalty," wrote the following:
"Common sense, lately bolstered by statistics, tells us that the death penalty will deter murder, if anything can. People fear nothing more than death. Therefore, nothing will deter a criminal more than the fear of death. Death is final. But where there is life there is hope...
Wherefore, life in prison is less feared. Murderers clearly prefer it to execution -- otherwise, they would not try to be sentenced to life in prison instead of death. (Only an infinitesimal percentage of murderers are suicidal.) Therefore, a life sentence must be less deterrent than a death sentence. And we must execute murderers as long as it is merely possible that their execution protects citizens from future murder."
Lewis Franklin Powell, Jr., LLM, late Justice of the US Supreme Court, in a June 29, 1972 Furman v. Georgia dissenting opinion, stated:
"On the basis of the literature and studies currently available, I find myself in agreement with the conclusions drawn by the Royal Commission [Report on Capital Punishment, 1949-1953] following its exhaustive study of this issue:
'The general conclusion which we reach, after careful review of all the evidence we have been able to obtain as to the deterrent effect of capital punishment, may be stated as follows. Prima facie, the penalty of death is likely to have a stronger effect as a deterrent to normal human beings than any other form of punishment, and there is some evidence (though no convincing statistical evidence) that this is in fact so.'"
H. Lee Sarokin, LLB, former US District Court and US Court of Appeals Judge, wrote in his Jan. 15, 2011 article "Is It Time to Execute the Death Penalty?” on the Huffington Post website:
"In my view deterrence plays no part whatsoever. Persons contemplating murder do not sit around the kitchen table and say I won't commit this murder if I face the death penalty, but I will do it if the penalty is life without parole. I do not believe persons contemplating or committing murder plan to get caught or weigh the consequences. Statistics demonstrate that states without the death penalty have consistently lower murder rates than states with it, but frankly I think those statistics are immaterial and coincidental. Fear of the death penalty may cause a few to hesitate, but certainly not enough to keep it in force..."
Michael L. Radelet, PhD, Sociology Professor and Department Chair at the University of Colorado-Boulder, wrote in his 2009 article "Do Executions Lower Homicide Rates?: The Views of Leading Criminologists” in the Journal of Criminal Law and Criminology:
"Our survey indicates that the vast majority of the world’s top criminologists believe that the empirical research has revealed the deterrence hypothesis for a myth... 88.2% of polled criminologists do not believe that the death penalty is a deterrent... 9.2% answered that the statement '[t]he death penalty significantly reduces the number of homicides' was accurate... Overall, it is clear that however measured, fewer than 10% of the polled experts believe the deterrence effect of the death penalty is stronger than that of long-term imprisonment... Recent econometric studies, which posit that the death penalty has a marginal deterrent effect beyond that of long-term imprisonment, are so limited or flawed that they have failed to undermine consensus.
In short, the consensus among criminologists is that the death penalty does not add any significant deterrent effect above that of long-term imprisonment."
The American Civil Liberties Union (ACLU), in its Apr. 9, 2007 website presentation titled "The Death Penalty: Questions and Answers," offered the following:
"The death penalty has no deterrent effect. Claims that each execution deters a certain number of murders have been thoroughly discredited by social science research. People commit murders largely in the heat of passion, under the influence of alcohol or drugs, or because they are mentally ill, giving little or no thought to the possible consequences of their acts. The few murderers who plan their crimes beforehand -- for example, professional executioners -- intend and expect to avoid punishment altogether by not getting caught. Some self-destructive individuals may even hope they will be caught and executed."
Jimmy Carter, 39th President of the United States, wrote in his Apr. 25, 2012 article "Show Death Penalty the Door” on the website of the Atlanta Journal-Constitution:
"One argument for the death penalty is that it is a strong deterrent to murder and other violent crimes. In fact, evidence shows just the opposite. The homicide rate is at least five times greater in the United States than in any Western European country, all without the death penalty.
Southern states carry out more than 80 percent of the executions but have a higher murder rate than any other region. Texas has by far the most executions, but its homicide rate is twice that of Wisconsin, the first state to abolish the death penalty. Look at similar adjacent states: There are more capital crimes in South Dakota, Connecticut and Virginia (with death sentences) than neighboring North Dakota, Massachusetts and West Virginia (without death penalties). Furthermore, there has never been any evidence that the death penalty reduces capital crimes or that crimes increased when executions stopped..."
John Lamperti, PhD, Professor Emeritus of Mathematics at Dartmouth College, wrote in his Mar. 2010 paper "Does Capital Punishment Deter Murder? A Brief Look at the Evidence," published at math.dartmouth.edu:
"[I]f there were a substantial net deterrent effect from capital punishment under modern U.S. conditions, the studies we have surveyed should clearly reveal it. They do not...
If executions protected innocent lives through deterrence, that would weigh in the balance against capital punishment's heavy social costs. But despite years of trying, this benefit has not been proven to exist; the only certain effects of capital punishment are its liabilities."
Tomislav Kovandzic, PhD, Associate Professor of Economic, Political, and Policy Sciences at the University of Texas at Dallas, wrote in his 2009 paper "Does the Death Penalty Save Lives?" in Criminology and Public Policy:
"Our results provide no empirical support for the argument that the existence or application of the death penalty deters prospective offenders from committing homicide... Although policymakers and the public can continue to base support for use of the death penalty on retribution, religion, or other justifications, defending its use based solely on its deterrent effect is contrary to the evidence presented here. At a minimum, policymakers should refrain from justifying its use by claiming that it is a deterrent to homicide and should consider less costly, more effective ways of addressing crime."
Jeffrey A. Fagan, PhD, Professor of Law and Epidemiology at Columbia University, said in his Feb. 1, 2006 testimony "Deterrence and the Death Penalty: Risk, Uncertainty, and Public Policy Choices" published on the website of the US Senate Committee on the Judiciary, Subcommittee on the Constitution, Civil Rights and Property Rights:
"Recent studies claiming that executions reduce crime... fall apart under close scrutiny. These new studies are fraught with numerous technical and conceptual errors: inappropriate methods of statistical analysis, failures to consider all the relevant factors that drive crime rates, missing data on key variables in key states, the tyranny of a few outlier states and years, weak to non-existent tests of concurrent effects of incarceration, statistical confounding of murder rates with death sentences, failure to consider the general performance of the criminal justice system... and the absence of any direct test of deterrence.
These studies fail to reach the demanding standards of social science to make such strong claims... Social scientists have failed to replicate several of these studies, and in some cases have produced contradictory results with the same data, suggesting that the original findings are unstable, unreliable and perhaps inaccurate. This evidence, together with some simple examples and contrasts... suggest that there is little evidence that the death penalty deters crime."
William C. Bailey, PhD, Professor of Sociology at Cleveland State University, in a June 1980 Social Forces study titled "Deterrence and the Celerity of the Death Penalty: A Neglected Question in Deterrence Research," wrote:
"No support whatsoever is found for the argument that the certainty, or celerity [speed], of the death penalty provides an effective deterrent to murder.
Although some possible limitations of this investigation have been identified, the consistency of the findings with earlier studies cannot be ignored. Nor can it be ignored that not a single reputable study has yet to demonstrate the death penalty to be a more effective deterrent to murder than alternative legal sanctions...
For these reasons, and because of the seriousness of the issue, I feel obliged to agree with most previous investigators. The evidence clearly suggests that the death penalty in our criminal justice system, at least for murder, will have to be justified on grounds other than its deterrence effectiveness."
John J. Donahue III, JD, PhD, Professor of Law at Stanford University, wrote in his Dec. 2005 article "Uses and Abuses of Empirical Evidence in the Death Penalty Debate" in the Stanford Law Review:
"Does the death penalty save lives?... [T]he death penalty - at least as it has been implemented in the United States - is applied so rarely that the number of homicides that it can plausibly have caused or deterred cannot be reliably disentangled from the large year-to-year changes in the homicide rate caused by other factors. As such, short samples and particular specifications may yield large but spurious correlations. We conclude that existing estimates appear to reflect a small and unrepresentative sample of the estimates that arise from alternative approaches. Sampling from the broader universe of plausible approaches suggests... reasonable doubt about whether there is any deterrent effect of the death penalty... There are serious questions about whether anything useful about the deterrent value of the death penalty can ever be learned from... the data that are likely to be available."
Thurgood Marshall, LLB, late Justice of the US Supreme Court, in a June 29, 1972 Furman v. Georgia concurrent opinion, stated:
"It is generally agreed between the retentionists and abolitionists, whatever their opinions about the validity of comparative studies of deterrence, that the data which now exist show no correlation between the existence of capital punishment and lower rates of capital crime.
Despite the fact that abolitionists have not proved non-deterrence beyond a reasonable doubt, they have succeeded in showing by clear and convincing evidence that capital punishment is not necessary as a deterrent to crime in our society.
In light of the massive amount of evidence before us, I see no alternative but to conclude that capital punishment cannot be justified on the basis of its deterrent effect."