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October 7, 2009

"Prison Population and Crime"

The title of this post is the title of this new criminology paper that I justice noticed via SSRN.  Here is the abstract of a paper that seems like a must-read for any and everyone who wants to make assertions about the relationship between incarceration rates and crime:
This is a critical review of the literature concerning the impact of prison populations on crime. It summarizes 44 time series studies that use prison population in the crime equation, emphasizing problems of simultaneity and disaggregation bias. It briefly reviews studies that estimate the incapacation impact of prisons by using criminals' individual crime rates, emphasizing problems caused by skewness of the crime rates and their relationship with arrest rates. Almost all the numerous problems with prior research bias results towards finding that prisons have limited impacts, and once the problems are addressed the best estimate of the elasticity of prison populations on crime is about 1.0.

October 7, 2009 at 08:18 AM | Permalink


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Is the existing research on the effect of imprisonment on crime biased against finding an effect? Is the research cited with such confidence by the let-em-out crowd wrong?On SSRN is a new study by Thomas Marvell of Justec Research. Here... [Read More]

Tracked on Oct 7, 2009 11:34:18 AM


Is the point, that, for every one person put in prison, one crime is deterred?


Posted by: NLO | Oct 7, 2009 9:36:45 AM


If a community has 500 criminals that commit an average of two crimes per month and 10% of the criminals are in jail at any given time incapacitation will reduce the total number of crimes per year by 10%. The elasticity is (10% crime reduction)/(10% incarcerated) = 1.0. This means that deterrence is not a significant factor. Jail for a hardened criminal is an inconvenience not a deterrence.

Posted by: John Neff | Oct 7, 2009 10:10:21 AM

This author concludes that his elasticity estimate shows "that prisons are worth the costs, but other researchers believe that the elasticity is much smaller and that crime prevention money is best spent elsewhere."

Posted by: Kent Scheidegger | Oct 7, 2009 11:53:07 AM

Leave aside the masssaging of massaged data from biased left wing academics.

The study uses reports of crime, not victimization surveys. There may be 10 rapes for every one reported. Even murder may be under-reported. There are 17,000 murders. However, there are 100,000 missing persons reports that are not resolved each year. The murder rate may be 5 times bigger than reported.

That multiplies the value of incapacitation. If you were to sue someone for the crimes listed, as intentional torts, with triple the medical bills for serious injuries, rapes, batteries, murders would generate $millions in verdicts, each. The value of the suffering of poor people is the same as that of rich people.

Assume 100 index felony crimes a year per criminal. Assume each is worth only $10,000 in damages. You are preventing $million in damages by spending $30,000 a year for prison. That is a 3000% return on investment, guaranteed, no risk to the capital.

Only 123D would be a better investment. We know in lawyer residential neighborhoods, there is no 123D. There is only 1D. The police kill the criminal at the scene. There is virtually no crime in lawyer residential neighborhoods. Shoplifting makes the papers, only a few miles from Fallujah on the Potomac.

Posted by: Supremacy Claus | Oct 7, 2009 2:05:43 PM

The most troubling note in the paper is that it states: "The paper studies only prison populations, and not other forms of incapacitation, such as jails, juvenile institutions, hospitals, mental institutions, and military stationed overseas. These seldom have adequate data, and the people involved are usually less criminally active than those sent to prison."

Five years ago, this would have seemed a plausible dismissal. But, it smacks of deliberate indifference when the hottest research in the field marshals evidence to show that the aggregate institutionalization rate, including mental institutions, is a much better predictors of crime rates than prison populations alone, using a collectition of that just the data that this study says is inadequate with little analysis.

From a cause and effect point of view, aggregate incarceration is a mysterious measure. Mental institution inmates are very different demographically and in terms of criminal histories from prison inmates. But, if this measure works when it comes to predicting crime rates, we should be asking why, not dismissing the evidence.

Posted by: ohwilleke | Oct 7, 2009 4:03:46 PM

Most criminals support themselves from their misdeeds. They don't work 9-5 jobs-that drudgery is relegated to "chumps". Few can support themselves and their girlfriends with two crimes a month. Self- report surveys show a much higher criminal incidence per actor.

Accordingly, this study undervalues the worth of incapacitation.

Posted by: mjs | Oct 7, 2009 5:00:33 PM

TY for the responses.


Posted by: NLO | Oct 8, 2009 2:09:01 AM

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