The Wall Street Journal has an OpEd by Roy Adler and Michael Summers, "Capital Punishment Works." Both are at Pepperdine University; Adler is a marketing professor, Summers a quantitative methods professor.
There is a small group of academics who purport to find a deterrent effect through the death penalty. I'm not aware of any serious study that actually demonstrates one. I look forward to seeing a rebuttal from Jeffrey Fagan, the Columbia law professor who has written extensively on the flaws of this research and the lack of evidence of any deterrent. Here's the opening of the Adler, Summers OpEd:
Most commentators who oppose capital punishment assert that an execution has no deterrent effect on future crimes. Recent evidence, however, suggests that the death penalty, when carried out, has an enormous deterrent effect on the number of murders. More precisely, our recent research shows that each execution carried out is correlated with about 74 fewer murders the following year.
For any society concerned about human life, that type of evidence is something that should be taken very seriously.
The study examined the relationship between the number of executions and the number of murders in the U.S. for the 26-year period from 1979 to 2004, using data from publicly available FBI sources. The chart nearby shows the number of executions and murders by year. There seems to be an obvious negative correlation in that when executions increase, murders decrease, and when executions decrease, murders increase.
In the early 1980s, the return of the death penalty was associated with a drop in the number of murders. In the mid-to-late 1980s, when the number of executions stabilized at about 20 per year, the number of murders increased. Throughout the 1990s, our society increased the number of executions, and the number of murders plummeted. Since 2001, there has been a decline in executions and an increase in murders.
It is possible that this correlated relationship could be mere coincidence, so we did a regression analysis on the 26-year relationship. The association was significant at the .00005 level, which meant the odds against the pattern being simply a random happening are about 18,000 to one. Further analysis revealed that each execution seems to be associated with 71 fewer murders in the year the execution took place.
The deterence index is here.
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