Does Capital Punishment Deter Crime? - Island of Sanity

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Does Capital Punishment Deter Crime?


Advocates of capital punishment routinely argue that statistics prove that it deters crime. Opponents of capital punishment just as routinely argue that statistics prove that it does not.

I suppose a naive person might find this disagreement puzzling. Even if we cannot agree on moral questions, surely we could at least agree on basic facts. I mean, it would be understandable if an anti-capital punishment person said that, yes, it does deter crime, but it is still wrong because it is cruel and barbaric; or if a pro-capital punishment said, okay, it doesn't deter crime any more than life imprisonment or some other punishment, but it is still right because it is just. But can't we at least agree on the underlying facts?

But as I'm sure we're all aware these days, you can twist statistics to prove almost anything. Statisticians have developed many sophisticated techniques to carefully analyze data. People with a point to prove can abuse these techniques to distort the data.

But I'm a simple guy, so I decided to look at the simple statistics. Let's just look at the raw numbers: no clever analysis, no involved mathematical manipulation, just look at the numbers.

So, using statistics from the United States Department of Justice website, here's my graph number 1: The homicide rate for each year since 1950.1 The rate is given as the number of homicides for every million people.

Graph 1: Homicide Rate

A casual glance at this graph clearly shows that homicide rates increased sharply beginning about 1965 or 1966, they took a steep dive from 1980 to 1985, started back up again until 1991 - 1992, and now appear to be inching down.

Surely a reasonable, concerned person could ask if there is any apparent cause for the sudden sharp increase in the late 60's. And surely we could look with hope at the drop in the early 80's, and ask if there was not something that was happening then that we could reproduce.

So let's look at another graph. Graph number 2 shows the homicide rate, just as above, and on top of this I show the number of cases where capital punishment was imposed.2

Graph 2: Homicide Rate vs Executions

Note the interesting correlations. The number of executions plummeted from 47 in 1962 to 2 in 1967 to zero in 1968. The homicide rate, which had been holding steady around 50 throughout the 50's, started up in 1965, just two years after executions began their plummet. The biggest increase in one year came in 1967, the same year that the last person was executed.

So okay, maybe this was simply a coincidence. Capital punishment was reinstated a decade later. What happened then?

In 1976 the Supreme Court issued several decisions in which they basically backtracked and again allowed capital punishment. (They didn't quite say that they were changing their minds or admitting error, but rather that the flaws which they had discovered in the previous capital punishment laws had now been corrected.) The first person was actually executed in 1977. In the very year of these Supreme Court decisions, the homicide rate plummeted. But no more than two people were actually executed in any one year through 1982, and so perhaps criminals concluded that the danger of execution was remote, and the homicide rate crawled back up. Then the number of executions suddenly went up in 1983, and in that year the homicide rate showed its biggest one-year drop. With the sudden surge in executions in 1996, the homicide rate again fell.

Indeed, just looking at this graph we can see that the homicide rate is almost the mirror image of the number of executions. Consistently when the number of executions goes down, the homicide rate goes up, and when the number of executions goes up, the homicide rate goes down. The only major exception to this is the fall in homicides in 1976, which came before executions re-started. But this is easily explainable by the fact that the court decisions allowing executions to resume came a year or two before executions actually did resume. Criminals may have been responding to press reports that capital punishment was once again going to take place, in advance of it actually happening.

I'm sure that opponents of capital punishment will say that my analysis here is too simplistic; that I have failed to take other factors into account; that this correlation between execution rates and homicide rates is pure coincidence, and that other factors explain why homicide rates went up and down at these times that had nothing to do with the number of executions.

To which I reply, Well, maybe, but I think you have an awfully hard sell. If there was just one point of correlation, it might be explained by coincidence. That is, if the homicide rate had gone up when capital punishment was abolished, but when capital punishment was re-instated the homicide rate had remained unchanged, or had gone up further, one might reasonably say that the first correlation was simply coincidence. But when we can clearly see that the two numbers mirror each other, consistently over a period of almost fifty years, attributing this to coincidence gets pretty hard to believe.

The obvious conclusion from looking at the statistics, without any fancy "analysis" or "factoring out of other factors", is that capital punishment does deter murder.


Footnotes

1. Source: United States Department of Justice, Bureau of Justice Statistics. "Homicide rates from the Vital Statistics." http://www.ojp.usdoj.gov/bjs/glance/hmrt.txt (March 1998). They in turn give the source of their data as the "National Center for Health Statistics, Vital Statistics". They give the homicide rate per 100,000 people -- I have adjusted this to "per million".

2. Source: United States Department of Justice, Bureau of Justice Statistics. "Number of persons executed in the United States, 1930-1997." http://www.ojp.usdoj.gov/bjs/glance/exe.txt (March 1998). They in turn give their source as "Capital Punishment, 1996, December 1997, NCJ-167031". The figures I had available did not distinguish between executions for murder and executions for other crimes (such as rape or treason), so in that sense it could be said that comparing these execution rates to the homicide rate is not entirely fair. But on the other hand, one might reasonably suppose that if a man is executed for rape, this could have as much deterrent affect on potential murderers as it has on other potential rapists.


Afterword

Lest I be accused of the same offense of which I accuse others, I will here freely discuss how I selected the data which I present.

I used homicide rate, i.e. homicides per million people, rather than the simple number of homicides, for two reasons. One, the data from the Department of Justice presented the numbers that way, so it was easiest to just take their numbers as given rather than looking up the population of the country each year and computing the simple number. (And I also would have run into the problem of possibly using different population statistics than the Department of Justice did, and thus introducing errors into the data.) Second, this is a good way to present the data anyway as it reflects the likelihood that any one person will decide to commit murder, which is the question under consideration. A graph of the simple number of murders would presumably show an overall upward trend reflecting growing population, and thus masking any deterrence or lack of deterrence.

On the other hand I used the simple number of executions rather than any "execution rate". Arguably it would be more accurate to plot executions as a percentage of the number of homicides, to show the probability that any given murderer would, in fact, be executed. I didn't do this for the simple reason that the Department of Justice figures did not present the numbers this way, and to compute them I would have had to convert homicide rate to number of homicides, and then compare this number to number of executions. This would have involved a lot of calculation using statistics from other sources, and so would not only have been a lot of work but could have introduced errors as mentioned above.

I converted homicide rates from homicides per 100,000, as the Department of Justice tabulates them, to homicides per million, simply to allow me to plot both homicide rates and number of executions on the same scale. That is, this conversion put the homicide rates in the 50 to 100 range or so, and executions were in the 0 to 100 range, so this conversion made it possible to plot both on the same graph without one being reduced to a line barely distinguishable from zero.

A more serious criticism could be leveled at my selection of the time range to include. I could not find any data on executions before 1930 or after 1996, so that was the widest possible range I could use. Clearly I had to go before the mid-60's to get before-and-after abolition comparisons, so going back to 1950 seemed about the shortest range to give meaningful numbers for comparison, and I went through the latest numbers because we surely want to see where things are right now.

Lest you wonder, analysis of earlier numbers reveals that the homicide rate went up sharply in the 20's and early 30's and fell in the late 30's and 40's. As I don't have data on executions before 1930, I cannot say if there is any correlation between the execution rate then and this increase. There were increasing numbers of executions in the late 30's as the homicide rate was coming down, but the correlation is nowhere near as obvious or dramatic as it is for the time period I discuss in the body of this article. Thus, I conclude that the movement of homicide rates in the 30's probably cannot be entirely explained by any deterrent effect of capital punishment, but must be at least partly attributed to other factors. I do not see this as in any way a refutation of the point of this article: neither I nor any one else I have ever heard is claiming that the deterrent effect of capital punishment is the only thing which affects homicide rates, merely that it is an import factor. No one denies that there could be other factors.

If anyone wants to accuse me of "cooking the data" to bias the results, based on the above or other considerations, that is your privilege. But I think in fairness you must show some equally simple, defensible selection of data that shows no correlation between capital punishment and murder rates. Otherwise, I think you can fairly be accused of saying simply, "That data must be invalid because it does not agree with what I just know must be true. No further analysis is necessary."

© 1998 by Jay Johansen


Comments

PJ Oct 10, 2010

Please forgive my horrible typing. I am probably the world's worst typist, and am a real novice at the computer. I looked up the subject of Capitol Punishment, and came across your site. I am not arguing that you are wrong and I am right. I just recall back around 1976 I gave a speech in college against Capitol Punishment. I actually won the debate with the other speaker. According to my teacher I had done my homework. I actually, at first won by default, as the man who was giving the opposite view never showed up. He did however, give it a few days later, still lost the speech. I recall the teacher wanted us to give Pro and Con speeches. He gave different ideas for speeches, wanted students to volunteer, and if we didn't , he would assign us. I found the subject interesting, so volunteered to speak out against Capitol Punishment. I recall ending my speech with a statement by a prison Warden, who basically said that Capitol Punishment did NOT deter crime. Of course, it was just his opinion. I recall his name was something like Warden Gordon F. Kirchway, or something like that. I don't have the book, so can't recall his exact words, yet what he said made sense to me at the time. He started out by saying something like, 'Who exactly does Capitol Punishment deter'? You take the husband, who discovers his wife in bed with another man. He finds a weapon nearby, kills them both. He does it in a fit of rage. He doesn't stop and think, I had better not do this, I could be executed. He does it in a fit of rage. Then he mentioned the mentally ill. they are mentally ill, they can't help it. Then the sly person, who plans it. they think they are so smart, or think they are, they just KNOW that they are not going to get caught. in the end, he says something like, "exactly who does capitol punishment deter?the normal law abiding people like you or me, WHO WOULDN'T DO IT ANYWAY" It made sense at the time to me. he actually said that it DOESN'T deter anyone. again, a person, in a fit of rage, well, they are in a fit of rage. They don't think. then the ones who are crazy{My words} the ones who plan it down to the last detail. They think they are so smart, there's no way they are going to get caught. I know those are not his EXACT words, as I said, I read that part ofv the book back in 1976. I believe his name was Gordon kirchway, I may not have his name right, but very close. the speech teacher went on to say, at that time that it was proven, I believe in the state of Illinois, to NOT DETER CRIME. just thought you might find this interesting. I realize you have really done research on the subject. I did a little speech many years ago, and at that time he did mention Illinois, at least I think he said Illinois.

Joel Dec 2, 2011

I was directed to your web site by the Mirror of Justice blog, which serves Catholic legal experts: general professors at Catholic law schools. I am not a lawyer however. I am an economist, who worked with Isaac Ehrlch in grad school, and ave an interest in various topics in law as a result.

I scanned your note on the death penalty. The most convincing empirical research is the early work of Isaac Ehrlich, and more recent work by Paul Rubin and Hashem Dezhbakhsh. Isaac is now the chairman of the economics department at the University of Buffalo (SUNY Buffalo). Rubin and Dezhbakhsh are colleages in the department of economics of Emory University. If you want to pursue this topic, you should probably contact them for references. I have one paper with Isaac, a concept paper, but for many years now I have been out of academia and working as a commodity speculator. There is an enormous amount of trash pseudoresearch on this topic, but this two sources are solid and reliable. This entire field of research started with Gary Becker (Nobel Laureate), who was Isaac's thesis advisor.

I would love to compare notes with you. I'm largely retired and spend my time writing, like you. You can find me and my firm on the web at www.logisticresearch.com.

Ray Aug 10, 2012

I recently came across your webpage discussing whether or not capital punishment deters crime, and thought I should contact you about the topic.

Fifteen years ago, I wrote a paper in College reviewing the same data and drawing the same conclusions. It was a compelling correlation. A crime and it's deterrent lined up perfectly over multiple decades. When the punishment is removed, the behavior increases. When the deterrent is reapplied the misdeed declines. It was convincing, and I was happy to apply these points to discussions with anyone on the other side of this issue.

Then last night I heard something that changed my mind about this position I had held my entire life. And it wasn't just any position. It was a belief I was proud to maintain. It contrasted sharply with the majority of my political leanings, providing me with a comforting sense of centrism.

The Baby Boomer generation started in the late 1940's - twenty years before the death penalty was eliminated in the United States. This places the boomer population squarely within the the young male demographic most prone to violence right when the homicide rate starts to skyrocket. The murder rate decline in the 80's coincides with Boomer males entering their thirties. The population bulge of young men had begun moving into a more sedentary phase of their lives where they were less likely to engage in violence.

Young males from fourteen to thirty are the most likely people to commit a murder. The homicide rate was demographically bound to surge and decline when it did, no matter what disincentives were being applied. The compelling link between capital punishment data and the homicide rate may be merely coincidental. The fifteen year experiment with death penalty abolition is an invalid data sample for it's potential affect. Additional data sets would be needed before drawing any conclusions.

Nikki Nov 19, 2012

Hi, Im doing a speech in class and i need accurate sources to cite, would you mind telling me the sources that you got the statistics from for the chart posted on death penalty rates please?

Jay Johansen Nov 20, 2012

Scroll down to where it says "footnotes" and it gives the URLs of my sources. Short answer: the Bureau of Justice Statistics, an agency of the United States Department of Justice.

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