Living the Scientific Life (Scientist, Interrupted)

To Kill or Not To Kill?

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I am a person who argues against the death penalty for ethical and economic reasons (I won’t get into those here), but I was quite surprised to learn that one argument that has been made against the death penalty (but not by me) seems to have been refuted; whether the death penalty serves as a deterrent to murder. In fact, a series of scientific studies published during the last five or six years have shown that between three and 18 lives could be saved by the execution of each convicted killer. Further, if executions were sped up, the deterrent effect would be strengthened.

“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.”

“If it’s the case that executing murderers prevents the execution of innocents by murderers, then the moral evaluation is not simple,” observed University of Chicago’s Cass Sunstein. “Abolitionists or others, like me, who are skeptical about the death penalty haven’t given adequate consideration to the possibility that innocent life is saved by the death penalty.”

Nor have I.

Basically, these studies concluded;

  1. Each execution deters an average of 18 murders, according to a 2003 nationwide study by professors at Emory University. (Other studies have estimated the deterred murders per execution at three, five and 14).
  2. The Illinois moratorium on executions in 2000 led to 150 additional homicides over four years following, according to a 2006 study at the University of Houston.
  3. Speeding up executions would strengthen the deterrent effect. For every 2.75 years cut from time spent on death row, one murder would be prevented, according to a 2004 study by an Emory University professor.

Even though these studies’ findings surprised me, I was not the least surprised by the last finding (speeding up executions increases their deterrent effect). Of all the seeming findings, that one makes the most sense to me.



  1. #1 Oran_Taran
    June 10, 2007

    Funny, that last one was what surprised me most. Do most people/murderers really know the average time someone spends in death row?

  2. #2 Jim
    June 10, 2007

    I believe that if you Murdered you should no matter what expect to be killed.Not sit in prison until your so tired of it your ready to jump onto the table to do it.It should be done ASAP!!!Can be more Humane than themselves and show mercy to let them say goodbye to the family not for them though, but for the familys I can imagine how hard it is to have someone of your family being killed by death penalty.The victoms family should be able to face them also and let them say whatever they want to help them vent and get on with their lives.

  3. #3 Josh
    June 10, 2007

    The problem is this: what about those who are wrongly convicted? How many innocent deaths are acceptable?

    As for speeding up the process, consider the dozen of people proven innocent by forensic techniques (like DNA testing) that did not exist when they were convicted. They could all be dead if we executed convicts more quickly.

  4. #4 Doug Alder
    June 10, 2007

    Strange – here in Canada the per capita number of homicides has consistently fallen since the death penalty was eliminated back around ’76.

  5. #5 daedalus2u
    June 10, 2007

    How many innocent deaths are acceptable?

    Presumably every innocent death is equivalently unacceptable. So deaths due to murder are exactly as unacceptable as deaths due to innocent people being executed. The “optimum” solution, is then to minimize the sum of innocent deaths due to murder and innocent deaths due to innocent people being executed.

    If executing a person saves 18 lives, obviously not enough people are being executed. Executing a guilty person is better because it saves 18 and doesn’t cost anything. Executing an innocent person saves 18 but costs 1 for a net gain of 17. The number of innocent people being executed should be increased until the balance is one-for-one. Guilty people can always be executed because even if the deterrent effect is near zero, as long as it is positive it is “worth” doing. However in places like Iraq, where revenge killings are common, it might actually be negative, that is executing someone may lead to more deaths. You would want to make sure that didn’t happen here.

    Of course, how the innocent people to be executed are chosen, likely will make a difference as to the deterrant effect of their deaths.

    How about just take people who have been convicted of something and kill them until the marginal deterrant rate reaches the “optimum”? Start with the most serious crimes, or the longest sentences and work your way down. That would reduce overcrowding, and maybe deter other crimes too.

    I would bet that you would reach the marginal deterrant rate long before you exhausted the prison population. If you didn’t, than you could start on other populations.

    (sarcasm off)

    There are other ways of reducing the murder rate. Regions with high employment, high education and high economic prosperity tend to have fewer murders. Maybe we should try that first?

  6. #6 Tara C. Smith
    June 10, 2007

    Hey grrl, don’t suppose you know where any of these studies were published? I’d love to dig into the actual research, but of course the article doesn’t give the journals…

  7. #7 Chris
    June 10, 2007

    We covered this in my Social Psych course however my professor said that although studies do show that after executions there is a drop in murders over the next couple of days that within weeks murders increase higher than before the execution and then return to the normal murder rate prior to the execution. Basically canceling out any effect the execution had as a deterrent. I don’t have the information with me currently however I can go look for it. Hopefully I worded it correctly. My professor may have also been biased in his statement as he is opposed to the Death penalty.

  8. #8 Chris
    June 10, 2007

    It should be noted that I took this course about a year ago so this study was not present at the time. So we didn’t cover this study but other studies on the death penalty.

  9. #9 Library Diva
    June 11, 2007

    I was surprised to hear this too. I am also against the death penalty, and in the Crime and JD class I took in high school, the teacher told us on the very first day that most people who commit crimes think that they’re either justified or they’ll get away with it.

    I didn’t study this at any higher level and don’t know about the veracity of it, but my anecdotal experience has borne that out: “WTF…it’s been 55 for the past 5 miles, now it’s gone down to 40 for no apparent reason? That’s ridiculous. I’m not slowing down!” “Come on, dude, it’s Friday night, the cops are all out dealing with REAL criminals, man, now quit worrying and pass that bong!” “I’ll just keep this beer in my coat pocket and I’ll be careful that there are no cars coming when I drink it, I’ll probably get away with it if I’m careful…” “Dude, we’re old enough to vote, we’re old enough to smoke, we’re old enough to die for our fucking country…we DESERVE this beer!” So I don’t see how any punishment can really serve as a deterrent for most people, since they’re generally thinking they’ll either get away with it or that the judge will see it their way, should they be unlucky.

  10. #10 llewelly
    June 11, 2007

    Tara: Publications of Naci Mocan one of the named researchers, including Getting Off Death Row. Abstract:

    This paper merges a state-level panel data set that includes crime and deterrence
    measures and state characteristics with information on all death sentences handed
    out in the United States between 1977 and 1997. Because the exact month and year
    of each execution and removal from death row can be identified, they are matched
    with state-level criminal activity in the relevant time frame. Controlling for a variety
    of state characteristics, the paper investigates the impact of the execution rate, com-
    mutation and removal rates, homicide arrest rate, sentencing rate, imprisonment rate,
    and prison death rate on the rate of homicide. The results show that each additional
    execution decreases homicides by about five, and each additional commutation in-
    creases homicides by the same amount, while an additional removal from death row
    generates one additional murder. Executions, commutations, and removals have no
    impact on robberies, burglaries, assaults, or motor-vehicle thefts.

    Emphasis mine. It was published in the Journal of Law and Economics. Although otherwise not contradicting the article, this study disagrees with the findings claimed for the Emory University study (‘Each execution deters an average of 18 murders…’), which I was not able to find.
    I’ve no means to judge the quality of either the paper or the journal.

  11. #11 Jean Watson
    June 11, 2007

    Those dismal economists at it again, eh?

    Ethics by numbers? pfffft.

  12. #12 Bob O'H
    June 11, 2007

    This sort of study rings all sorts of alarm bells – it’s correlative, so there could be a lot of other confounders in the data. I think we would need to see data from several different countries.

    I did find this an odd comment in the report, when it was raising some criticisms:

    And several argue that there are simply too few executions each year in the United States to make a judgment.

    Eek! I guess a randomised trial is out of the question then.

    Tara – the lead author’s list of publications is here, and it looks like this is the pdf of the ‘main’ paper, and includes links to the data. It’s possible that the results are just an effect of the drop in murder rates and rise in executions in the 1990s: it would be interesting to see an analysis without that data (I’d be happy to help with a re-analysis of the data, but I’m not going to format it all together first!).


  13. #13 Chris' Wills
    June 11, 2007

    I’m not sure if the punishment actually is much of a deterrent, for the reasons Library Diva posted.

    It is the fear of being caught and if people “know” that the likelihood of being caught and convicted is low they are more likely to break the law. For certain classes of law-breaking the clean up rates are abysmal, house breaking for example.

    We also have the fact that some laws are considered wrong headed, stupid, immoral etc and people feel justified in breaking these laws sacrificing (in some cases literally) themselves for the greater good.

    On the legal executions issue:
    1) It is a poor idea as we cannot be sure that we aren’t executing an innocent person. What is an acceptable error rate?
    2) If someone has killed once, say in a bank robbery, then they have no reason to surrender. They can only be executed once so it doesn’t make sense for them to surrender peacefully.

  14. #14 Roy
    June 11, 2007

    People like to think that our legal system works well. At the same time, they know it is severely broken: 99% of cases get convictions without going to trial. Why? Because if the prosecutor had to try every case they would lose almost all of them, and the prosecutor would be fired.

    Say you are accused of killing someone. The cops threaten you with a death sentence for murder in the first, but offer you manslaughter, good for twenty to life. You didn’t kill anyone, but you believe the cops will make good on their promise, since you know that cops routinely lie, cheat, steal, plant evidence, buy perjury, and fabricate evidence. So you cop a plea, and take life-without.

    Now somebody comes along and presents an argument that quick death sentences will save lives.

    Hmm. How would someone measure such a thing? It cannot be done experimentally, because they’re not allowed to experiment.

    I don’t doubt somebody else has already explained the studied developments as due to things unrelated to penology.

    If somebody gets killed, some people want blood — anybody’s, it doesn’t matter who, just as long as somebody pays for the crime.

    In Jim Crow’s era, the ‘somebody’ was always a black man. It didn’t matter if the raped girl gave birth to an albino baby, it was always a black man ‘who done it’. Every time something bad happened, they hanged a black man.

    Today, the only people who will be killed as a legal penalty will be the poor.

    Once they are conveniently dead, then it won’t do any good to discover later they were innocent all along.

    Just to clear your head, assume that 90% of the time the police have the wrong guy. Is it worth murdering nine innocents just to make you feel better about the occasional actual culprit getting tortured to death?

    Both electrocution and lethal injection methods are torture, by the way. The pancuronium is a paralytic: it is there to prevent the person from screaming and writhing in pain. The fact that it is used at all is proof that everyone involved knows it is needed.

  15. #15 Nick Leaton
    June 11, 2007

    There is a nice way of controlling people killed by mistake.

    Make execution of a person who subsequently is found to be innocent, murder.

    Then you can execute the judge, the jury, the prosecution, and the executioners as murderers.

    By the logic used in the study, this would reduce the wrongful exections by a factor of 18 to 1.

  16. #16 cephyn
    June 11, 2007

    Do the studies discuss why Texas, which executes significantly more criminals than any other state, does not have a murder rate significantly lower than any other state? Are Texans just bad people?

    I am skeptical of these studies. And the Canada example is also good – this issue is far more complex than it may seem.

  17. #17 Chris' Wills
    June 11, 2007

    …Make execution of a person who subsequently is found to be innocent, murder.
    Then you can execute the judge, the jury, the prosecution, and the executioners as murderers……..
    Posted by: Nick Leaton

    I see a problem, how likely is the state to investigate possible innocence after execution if such a law was in place?

    If I was the law maker I’ld ensure that all executed people be cremated as well.

    There is the other issue, how likely would a jury be to find a person guilty in such a situation?
    It would result in more murders going free as jurors wouldn’t want to risk death because of their findings based on the evidence presented.

  18. #18 "GrrlScientist"
    June 11, 2007

    Tara; unfortunately, i do not have the references (thereby making this story suspicious) and it is doubtful that i can access the papers, unless someone sends them to me so i can have a go at them.

    i also find a lot to worry about with regards to these studies because they appear to be correlative only — not rigorous (although i cannot know, having not read the original work). also, they don’t discount the numbers of innocent people who are executed and the “cost” incurred as a result of those wrongful executions, and they ignore that violent crime is been shown to be a consequence of poverty and grossly unequal economic opportunities. thus, i find it difficult to accept the “fact” that the death penalty provides a deterrent effect against murder — especially when i think about texas, which resembles a human slaughterhouse in my mind, both with regards to the murder rate and the execution rate.

  19. #19 Bob O'H
    June 12, 2007

    Grrl – in the paper I linked to, they do account for poverty (e.g. income, and unemployment rate, p459). Whether this is sufficient I couldn’t say. I agree that the data is correlative, so one should be cautious about its interpretation. It might be interesting to look at it in more detail (most, if not all, of the data seems to be available online): there are a couple of oddities that could be checked, and I think more could be done with the within-state variation to look at the deterrence effect.


  20. #20 dirtmcgrit
    June 13, 2007

    Texas actually has a below average murder rate. It’s only twice that of Canada.

    The real question is how many lives you can save by lowering unemployment 0.1% , changing education policy, raising minimum wage 10 cents, or otherwise affecting income inequality.

  21. Re: Library Diva @ #9:

    I have been given to understand (sorry, don’t remember any references) that what makes the biggest difference in the deterrent effect is not the harshness of the punishment, but how likely offenders are to be punished. That is, if only an occasional criminal is pulled apart publically by wild horses and red-hot iron chains, people will think, “Yah, but they won’t catch me” and carry on with their crimes. If almost all criminals get slapped upside the head with a fish and sentenced to community service, the minimum level of delusion necessary to think you won’t get caught rises, and fewer people do crimes because the expected level of punishment has actually gone up.

  22. #22 stewart
    June 14, 2007

    Deltoid provides some interesting links on this. It’s worth noting that all of these studies look only at a short span of years, use somme interesting proxies, and are US-focused. Over a longer span of years, there is no evidence, and cross-national data is not convincing. Try this link for some thoughtful comments by a researcher in the area:

  23. #23 Valuethinker
    June 19, 2007


    Where do you get your murder rate data?

    AFAIK the highest murder rates in the US are all in southern and southwestern cities: so that would include Dallas metro and Houston (I think Phoenix is actually the highest). It is the north east that has the anomalously low murder rate (New York, and New England).

    So I am very surprised at your data.

    One possible explanation is that Texas has a relatively small Afro-American population (is that true?) and they have a murder rate far higher than the national average.

  24. #24 David Harmon
    June 19, 2007

    Well, an execution certainly prevents that person from killing anyone else… unless of course, you execute the wrong person.

    Given the state of criminal justice in America, and especially the prior administration of the death penalty, I have to consider that pragmatically, the death penalty is simply not a usable tool of justice in this country.

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