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Proponents of the death penalty often argue that the threat of being executed deters people from committing murder. Opponents of capital punishment say that's not true. Now, a panel at the National Research Council has looked into the question. And the panel finds that opponents and proponents have one thing in common. None of them has any real evidence to work with. NPR's Nell Greenfieldboyce reports on the findings.
NELL GREENFIELDBOYCE, BYLINE: This committee did not examine the moral arguments for or against the death penalty. Its job was to look at the science. And its new report has this advice for policy-makers: don't rely on any studies that make claims about the effect of the death penalty on murder rates, because the research to date is useless.
DANIEL NAGIN: We recognize that this conclusion may be controversial to some. But nobody 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 homicides, or actually increases homicides.
GREENFIELDBOYCE: Daniel Nagin chaired the committee. He's a public policy professor at Carnegie Mellon University. He says, the panel reviewed dozens of studies, and found fundamental flaws. None accounted for the possible effect of other punishments on homicide rates.
NAGIN: The real question is, does the death penalty deter more than other penalties, like life in prison. None of the research from the past 35 years addresses this problem.
GREENFIELDBOYCE: What's more, much of the available research assumes that people who might commit murder can accurately calculate their risk of being executed if they were convicted.
NAGIN: In reality, this is very difficult to do.
GREENFIELDBOYCE: Even researchers have a hard time determining that risk. And Nagin says, basically nothing is known about how potential murderers - whoever they might be - actually perceive their risk of execution. The report says it would be possible to design better studies to look at whether the death penalty has a deterrent effect, but they won't be quick or easy.
Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright National Public Radio.