Studies Show Death Penalty Deters

"[A] series of academic studies over the last half-dozen years ... count between three and 18 lives that would be saved by the execution of each convicted killer...

"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 homicides. ... "I oppose the death penalty. But my results show that the death penalty (deters) - what am I going to do, hide them?" [he said].

... [S]tudies like his are among a dozen papers since 2001 that capital punishment has deterrent effects. They all explore the same basic theory - if the cost of something (be it the purchase of an apple or the act of killing someone) becomes too high, people will change their behavior (forego apples or shy from murder).

... [T]hey look at executions and homicides, by year and by state or county, trying to tease out 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 following, according to a 2006 study by professors at the University of Houston.

- Speeding up 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.

... Some claim that the pro-deterrent studies made profound mistakes in their methodology, so their results are untrustworthy. Another critic argues that the studies wrongly count all homicides, rather than just those homicides where a conviction could bring the death penalty. And several argue that there are simply too few executions each year in the United States to make a judgment. ...

Several authors of the pro-deterrent reports said they welcome criticism in the interests of science, but said their work is being attacked by opponents of capital punishment for their findings, not their flaws.