The Statistical Impact Of Capital Punishment By Betsy Newmark

The Associated Press reports on some studies of the deterrent effect of capital punishment.

“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 homicides. “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 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 away from murder).

To explore the question, they 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.

Of course, these studies have their critics. There is certainly going to be a lot of debate over these results as they get more public scrutiny. But if these studies hold up, the moral debate over capital punishment gets even more troubling.

This content was used with the permission of Betsy’s Blog

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