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Research findings could alter debate on death penalty

Scientists see crime deterrence

Death penalty opponents outside Southern Ohio Correctional Facility in Lucasville protested James Filiaggi's execution in April. Filiaggi was convicted of the 1994 killing his former wife. (Scott Osborne/associated press)

NEW YORK -- Anti death penalty forces have gained momentum in the past few years, with a moratorium in Illinois, court disputes over lethal injection in more than a half-dozen states, and progress toward outright abolishment in New Jersey.

The steady drumbeat of DNA exonerations -- exposing flaws in the justice system -- has weighed against capital punishment. The moral opposition is loud, too, echoed in Europe and the rest of the industrialized world, where all but a few countries banned executions years ago.

What gets little notice, however, is a series of academic studies over the last half-dozen years that claim to settle a once hotly debated argument -- whether the death penalty acts as a deterrent to murder. The analyses say yes. They count between three and 18 lives that would be saved by the execution of each convicted killer.

The reports have horrified death penalty opponents and several scientists, who question the data and its implications.

So far, the studies have had little impact on public policy. New Jersey's commission on the death penalty this year dismissed the body of knowledge on deterrence as inconclusive.

But the fierce argument in academic circles could eventually spread to a wider audience, as it has in the past.

"Science does really draw a conclusion. It did. There is no question about it," said Naci Mocan, an economics professor at the University of Colorado at Denver. "The conclusion is there is a deterrent effect."

A 2003 study he co authored, and a 2006 study that re examined the data found that each execution results in five fewer homicides, and commuting a death sentence means five more . "The results are robust, they don't really go away," he said. "I oppose the death penalty. But my results show that the death penalty [deters]. What am I going to do, hide them?"

Statistical studies like his are among a dozen papers produced since 2001 that indicate that capital punishment has deterrent effects. They all explore the same basic theory -- if the cost of something ( for example the purchase of an apple or the act of killing someone) becomes too high, people will change their behavior ( forgo apples or refrain from murder).

To explore the question, they look at executions and homicides, by year and by state or county, trying to determine the impact of the death penalty on homicides by accounting for other factors, such as unemployment data and per capita income, the probabilities of arrest and conviction, and more.

Among the conclusions:

Each execution deters an average of 18 murders, according to a 2003 nationwide study by professors at Emory University. (Other studies have estimated the deterred murders per execution at three, five, and 14).

The Illinois moratorium on executions in 2000 led to 150 additional homicides over four years afterward, according to a 2006 study by professors at the University of Houston.

Shortening the waiting time for executions would strengthen the deterrent effect. For every 2.75 years cut from time spent on death row, one murder would be prevented, according to a 2004 study by an Emory University professor.

In 2005, there were 16,692 cases of murder and nonnegligent manslaughter nationally, and 60 executions.

The studies' conclusions drew a philosophical response from a well-known liberal law professor, Cass R. Sunstein of the University of Chicago. A critic of the death penalty, in 2005 he co authored a paper titled "Is Capital Punishment Morally Required?"

"If it's the case that executing murderers prevents the execution of innocents by murderers, then the moral evaluation is not simple," he told the Associated Press. "Abolitionists or others, like me, who are skeptical about the death penalty haven't given adequate consideration to the possibility that innocent life is saved by the death penalty."

Sunstein said that moral questions aside, the data needs more study. Critics of the findings have been vociferous.

Some contend that the studies with pro-deterrent conclusions made profound mistakes in methodology, so the results are untrustworthy. And several say that there are too few executions in the United States to make a judgment.

"We just don't have enough data to say anything," said Justin Wolfers, an economist at the Wharton School of Business who last year co authored a critique of several studies and said they were "flimsy."

"This isn't left vs. right. This is a nerdy statistician saying it's too hard to tell," Wolfers said. "Within the advocacy community and legal scholars who are not as statistically adept, they will tell you it's still an open question. Among the small number of economists at leading universities whose bread and butter is statistical analysis, the argument is finished."

Several authors of the pro-deterrent reports said their work is being attacked by opponents of capital punishment for their findings, not their flaws.