A Conflicting Deterrence Study

The Science blog at USA Today has, "Study: Executions might slightly lower homicide rates," posted by Dan Vergano.

Executions in Texas slightly lower homicide rates there, about five to 10 killings in the year afterwards, suggest criminologists.The executions also may displace homicides to nearby states, however.

"Does the death penalty save lives?," a study led by sociologist Kenneth Land of Duke University in the current Criminology journal, looked at executions in Texas from 1994 to 2005 and subsequent crime.  Criminologists, and Supreme Court cases, have debated the death penalty for at least four decades, the study notes, adding, "estimates of the deterrent effects of executions are highly sensitive to the model," used in the analysis.

In the study, the team looked at Texas, where about one-third of all executions have occurred nationwide since 1973, and where past researchers have disagreed on deterrent effects. Because legal decision led to greatly-increased executions in 1994, the researchers looked at cases starting with that year.

"We conclude that evidence exists of modest, short-term reductions in the numbers of homicides in Texas in the months of or after executions," the study concludes. Based on statistics, about 2.5 fewer murders than would have otherwise took place in Texas in the one to four months after an execution, where the state had 8,511 murders in 2005, according to the FBI. But the analysis statistics suggest the executions also displaced murders to later months and to other states, lowering the deterrent effect of each execution to 0.5 fewer murders in the next year.

Texas execution rates have raised controversy, heightened this year by reports of questionable arson evidence used in a prominent case detailed the year in the New Yorker magazine. Disagreement among criminologists will likely continue over the deterrent effect of executions...

Last week, a study conducted by UT Dallas researchers, noted here, showed no deterrent effect. 

I believe that the most accurate and succinct comment on the topic comes from Cass Sunstein and Justin Wolfers in their 2008 Washington Post OpEd, "A Death Penalty Puzzle," noted here:

In short, the best reading of the accumulated data is that they do not establish a deterrent effect of the death penalty.

Related posts are in the deterrence category index.