The National Research Council released a report this month titled Deterrence and the Death Penalty. It acknowledges the many studies concerning the deterrent effect of the capital punishment and the widely differing results of these studies. Some studies have found that use of the death penalty decreases the murder rate, some have found that it has no effect, and others have even found that it increases the murder rate.
The primary conclusion of this report, which neither supports or opposes the death penalty as public policy, is that the research to date is not informative about whether the death penalty decreases, increases, or has no effect on homicide rates. Its opinion is that "these studies should not be used to inform deliberations requiring judgments about the effect of the death penalty on homicide rates."
The report finds that these studies are all statistically flawed, do not consider the deterrence effect of alternative punishments, and use incomplete or implausible models of potential murders' perceptions of and response to the use of capital punishment.
The report only strengthens the common sense argument that potential murderers are often do not know whether their state has or uses the death penalty, and are even more unlikely to know the specifics of the state's capital punishment system and make an objective decision about whether the risk of execution outweighs the desire to commit the crime.
For now, this report says that recent research should not be used to make public policy decisions concerning the death penalty and it negates the validity of the argument that the deterrent effect of the death penalty will reduce crime rates.