Deterrence
The existence of a deterrence effect is disputed. Studies differ as to whether executions deter other potential criminals from committing murder or other crimes.
One reason that there is no consensus on whether or not the death penalty is a deterrent is that it is used so rarely - only about one out of every 300 murders actually results in an execution. In 2005 in the Stanford Law Review, John J. Donohue III, a law professor at Yale with a doctorate in economics, and Justin Wolfers, an economist at the University of Pennsylvania, wrote that the death penalty "... is applied so rarely that the number of homicides it can plausibly have caused or deterred cannot reliably be disentangled from the large year-to-year changes in the homicide rate caused by other factors... The existing evidence for deterrence... is surprisingly fragile." Wolfers stated, "If I was allowed 1,000 executions and 1,000 exonerations, and I was allowed to do it in a random, focused way, I could probably give you an answer."
Naci Mocan, an economist at Louisiana State University, authored a study that looked at all 3,054 U.S. counties over two decades, and concluded that each execution saved five lives. Mocan stated, "I personally am opposed to the death penalty... But my research shows that there is a deterrent effect."
Joanna M. Shepherd, a law professor at Emory with a doctorate in economics who was involved in several studies on the death penalty, stated, "I am definitely against the death penalty on lots of different grounds... But I do believe that people respond to incentives." Shepherd found that the death penalty had a deterrent effect only in those states that executed at least nine people between 1977 and 1996. In the Michigan Law Review in 2005, Shepherd wrote, "Deterrence cannot be achieved with a half-hearted execution program."
The question of whether or not the death penalty deters murder usually revolves around the statistical analysis. Studies have produced disputed results with disputed significance.[8] Some studies have shown a positive correlation between the death penalty and murder rates[9] - in other words, they show that where the death penalty applies, murder rates are also high. This correlation can be interpreted in either that the death penalty increases murder rates by brutalizing society, or that higher murder rates cause the state to retain or reintroduce the death penalty. However, supporters and opponents of the various statistical studies, on both sides of the issue, argue that correlation does not imply causation.
In recent years, a number of new studies have been published, mostly by economists, that statistically demonstrate a deterrent effect of the death penalty.[10] However, critics claim severe methodological flaws in these studies and hold that the empirical data offer no basis for sound statistical conclusions about the deterrent effect.[11]
Surveys and polls conducted in the last 15 years show that some police chiefs and others involved in law enforcement may not believe that the death penalty has any deterrent effect on individuals who commit violent crimes. In a 1995 poll of randomly selected police chiefs from across the U.S., the officers rank the death penalty last as a way of deterring or preventing violent crimes. They ranked it behind many other forms of crime control including reducing drug abuse and use, lowering technical barriers when prosecuting, putting more officers on the streets,and making prison sentences longer. They responded that a better economy with more jobs would lessen crime rates more than the death penalty (Deiter 23). In fact, only one percent of the police chiefs surveyed thought that the death penalty was the primary focus for reducing crime (Deiter 25).
However, the police chiefs surveyed were more likely to favor capital punishment than the general population.
Deiter, Richard. “The Death Penalty is not an Effective Law Enforcement Tool.” Ed. Stephen E. Schonebaum. Does Capital Punishment Deter Crime? San Diego, CA: Greenhaven Press, 1998
In addition to statistical evidence, psychological studies examine whether murderers think about the consequences of their actions before they commit a crime. Most homicides are spur-of-the-moment, spontaneous, emotionally impulsive acts. Murderers do not weigh their options very carefully in this type of setting (Jackson 27). It is very doubtful that killers give much thought to punishment before they kill (Ross 41).
But some says the death penalty must enforce even if the detterent effect is unsure, like John McAdams who teach political science in Marquette university : " If we execute murderers and there is in fact no deterrent effect, we have killed a bunch of murderers. If we fail to execute murderers, and doing so would in fact have deterred other murders, we have allowed the killing of a bunch of innocent victims. I would much rather risk the former. This, to me, is not a tough call. "
