The unpleasant truth for you is that as reported by The New York Times, CBS, and The Associated Press several studies, conducted by credible researchers, have found the death penalty provides a deterrent and saves lives and several notable economists have found the studies valid including a Nobel Laureate. You are on the wrong side of science.
Had you also read it, which you clearly have not, you would see that the only way it can work as a deterrent is if each State executes one person each year, because to get the deterrent effect, they had to lag the result and put in at least one execution each year, otherwise, they could not obtain that result. Had you read the study you keep citing, you would also see that by their calculations, what you are praising to rid of errors to apparently cut down on wrongful convictions and executions works against the deterrent effect.. So the study clearly states that removing people from death row or the death penalty has an opposite effect. Do you understand now? For it to work as a deterrent, even innocent people, who once convicted and placed on death row, should not be removed from said death row even if it is clear they are innocent. Worse yet and which is why the authors caution about the death penalty in their study (which you did not read), there is clear evidence of racial discrimination in the criminal justice system and it is not applied fairly or equally.
Although these results demonstrate the existence of the deterrent effect of capital punishment, it should be noted that there remains a number of significant issues surrounding the imposition of the death penalty. For example, although the Supreme Court of the United States remains unconvinced that there exists racial discrimination in the imposition of the death penalty, recent research points to the possibility of such discrimination (Baldus et al. 1998, Pokorak 1998, Kleck 1981). Along the same lines, there is evidence indicating that there is discrimination regarding who gets executed and who gets commuted once the death penalty is received (Argys and Mocan 2002). Given these concerns, a stand for or against capital punishment should be taken with caution.*
The manner in which these economists have attempted to skew the numbers to reach a deterrent effect is why the
National Academy of Sciences have been so scathing in their response to these studies, because their numbers and results contradict each other, are skewed and lagged to such a degree that they make no sense aside from trying to obtain a positive result, and because they consistently fail to take in all other variables that affect the death penalty.
There is no empirical basis for choosing among these specifications, and there has been heated debate among researchers about them, particularly on the number of years that should be lagged for the numerator and, even more so, for the denominator in order to best correspond to the relevant risk of execution given a death sentence in each state and year. This debate, however, is not based on clear and principled arguments as to why the probability timing that is used corresponds to the objective probability of execution, or, even more importantly, to criminal perceptions of that probability. Instead, researchers have constructed ad hoc measures of criminal perceptions. Consequently, the results have proven to be highly sensitive to the specific measures used. Donohue and Wolfers (2005) find, for example, that when reanalyzing the results in Mocan and Gittings (2003), using a 7-year lag implies that the death penalty deters homicide (4.4 lives saved per execution) but using a 1-year lag implies that the death penalty increases the number of homicides (1.2 lives lost per execution). Donohue and Wolfers (2005) question whether would-be murderers are aware of the number of death sentences handed down 7 years prior. Responding to these concerns, Mocan and Gittings (2010) argue that because executions do not take place the same year as a sentence is imposed, models with a 1-year lag are meaningless.
[...]
The fact that there is a mismatch between the numerator and denominator in the models used is perhaps best illustrated by the many state-year cases in which there are one or more executions the prior year but there were no death sentences imposed 7 years earlier. Researchers have made a variety of ad hoc removals or substitutions for these undefined cases including: replace with zero or treat as missing (Kovandzic, Vieraitis, and Boots, 2009); numerator set to zero regardless of denominator and non-zero numerator and zero denominator considered missing at random (Donohue and Wolfers, 2005; Mocan and Gittings, 2003, 2010); replace with most recent defined ratio (Zimmerman, 2004). These (and other) ad hoc adjustments highlight the general problem that the people who were sentenced to death 7 years earlier may be executed before or after the year in which executions are counted, and they are not the only people at risk for being executed in the current or prior year. Overall, the interpretation of this ratio is not clear at all, whether the denominator is lagged any particular number of years, and its relevance to the objective risk of execution for each state and year, let alone to the risk perceptions of potential murderers, is highly questionable.
Basing execution risk measures only on data on executions that have actually been carried out, as has been done in the research being discussed, could result in a serious underestimate of the eventual probability of execution for those given a death sentence. In addition, this fact raises serious questions about whether the risk of ever being executed after a death sentence is the most salient measure or whether additional information is salient, such as measures that consider expected time to death, expected living conditions while on death row, and in comparison, expected time to death during a long prison sentence and conditions while in prison in that state. (Of course, one can only speculate about which, if any, of these variables is salient for potential murderers.)
These many complications make clear that even with a concerted effort by dedicated researchers to assemble and analyze relevant data on death sentences and executions, assessment of the actual and changing objective risk of execution that faces a potential murderer is a daunting challenge. Given the obstacles to obtaining an objective measure of this risk, the committee does not find any of the measures used in the studies to be credible measures of the objective risk of execution given a death sentence. We also reiterate that it is not known whether there is a relationship between any of these measures or any more credible objective measure of execution risk, and the execution risk as perceived by potential murderers.
The study by the National Academy of Sciences is over 140 pages long and makes for interesting reading. Which I doubt you will read, because you prefer to stick to non-scientific news stories instead. Now, as a lawyer, I'd rather stick to science which clearly shows that the manner in which Mocan and Gittings and their economics cohorts obtained the results were skewed and completely unreliable. In fact, it is so bad that the Committee recommends the following about the studies by these economists:
In summary, the committee finds that adequate justifications have not been provided to demonstrate that the various time-series-based studies of capital punishment speak to the deterrence question. It is thus immaterial whether the studies purport to find evidence in favor or against deterrence. They do not rise to the level of credible evidence on the deterrent effect of capital punishment as a determinant of aggregate homicide rates and are not useful in evaluating capital punishment as a public policy.
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The committee concludes that research to date on the effect of capital punishment on homicide is not informative about whether capital punishment decreases, increases, or has no effect on homicide rates. Therefore, the committee recommends that these studies not be used to inform deliberations requiring judgments about the effect of the death penalty on homicide. Consequently, claims that research demonstrates that capital punishment decreases or increases the homicide rate by a specified amount or has no effect on the homicide rate should not influence policy judgments about capital punishment.
In fact, the results from the studies by the likes of Mocan and Gittings have had the National Academy of Sciences issue a warning in taking them seriously. And this isn't even considering the responses from
Criminologists and Lawyers, who also advised that the Mocan and Gittings study was flawed and explained why, and which was linked earlier on in this thread. That is the reality of a scientific and legal response to these studies. Sure, you may refuse to read them, just as you have yet to even read the study that was cited in the CBS news story you keep referring to, and instead relied solely on the abstract...
* H. Naci Mocan, University of Colorado at Denver, and R. Kaj Gittings, Cornell University, "Getting Off Death Row: Commuted Sentences and the Deterrent Effect of Capital Punishment", 46 Journal of Law arid Economics 453 (2003)