Is the Death Penalty a Deterrent?

From the AP via the Cincy Enquirer comes a story about whether executing criminals is a deterrent to future homicides:

…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….

"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 from murder).

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

More here, including rebuttals and rebukes from critics, an overview of past controversies, etc.

I am against the death penalty because I think the state should use the least amount of violence to protect people from criminals. That said, I think it's always worth knowing the actual effects of policy (or at least debating them). I've got no idea if the new research is better than older research that led to different conclusions. But it's certainly worth talking about (and in as broad a context as possible, one that factors in social factors that range beyond immediate effects on crime rates).