Impact of Incarceration on Crime

Reasonable Doubt: A New Look at Whether Prison Growth Cuts Crime

This is the first in a series of posts summarizing the Open Philanthropy review of the evidence on the impacts of incarceration on crime. The full report is available in PDF, Kindle, and ePub formats.

About when Chloe Cockburn joined Open Philanthropy to spearhead our grantmaking for criminal justice reform, I was tasked with reviewing the research on whether reducing the number of people in American jails and prisons might actually increase crime. In effect, we at Open Philanthropy asked ourselves: what if we’re wrong? What if our grantees win reforms that cut the number of people behind bars, and that pushes the crime rate up? How likely is that? And how likely is it that any increase would be large enough to overshadow the benefits of decarceration, which include taxpayer savings and expanded human freedom?

It may seem strange to launch a grantmaking program even as we question its empirical basis. But Open Philanthropy had already invested significant time in studying criminal justice reform as a cause. And practical decisions must always be made in the face of incomplete information, forcing people and organizations to exercise what Herbert Simon called “bounded rationality.” It can be boundedly rational to act on the information gathered so far, even as we gather more.

The final report reaches two major conclusions:

  • I estimate, that at typical policy margins in the United States today, decarceration has zero net impact on crime. That estimate is uncertain, but at least as much evidence suggests that decarceration reduces crime as increases it. The crux of the matter is that tougher sentences hardly deter crime, and that while imprisoning people temporarily stops them from committing crime outside prison walls, it also tends to increase their criminality after release. As a result, “tough-on-crime” initiatives can reduce crime in the short run but cause offsetting harm in the long run.
  • Empirical social science research—or at least non-experimental social science research—should not be taken at face value. Among three dozen studies I reviewed, I obtained or reconstructed the data and code for eight. Replication and reanalysis revealed significant methodological concerns in seven and led to major reinterpretations of four. These studies endured much tougher scrutiny from me than they did from peer reviewers in order to make it into academic journals. Yet given the stakes in lives and dollars, the added scrutiny was worth it. So from the point of view of decision makers who rely on academic research, today’s peer review processes fall well short of the optimal.

The rest of this post elaborates on those conclusions.

Deterrence Is De Minimis

This is the second in a series of posts summarizing the Open Philanthropy review of the evidence on the impacts of incarceration on crime. The full report is available in PDF, Kindle, and ePub formats.

As I explain in the intro post, in thinking about how incarceration affects crime rates, it is useful to distinguish between “before,” “during,” and “after” effects. The “before” effects of incarceration are deterrence: the prospect of jail or prison time may dissuade people from committing crime. Surely this must happen to some extent, but how much at current policy margins, is a question for research. The experimental and quasi-experimental studies I read and reproduced mostly said: not much.

Below, I review research on:

  • Laws criminalizing driving under the influence of alcohol;
  • a mass prison sentence suspension in Italy;
  • whether young people commit less crime as they obtain the age of criminal majority, when they first face the risk of adult-level sanctions;
  • California’s severe “Three Strikes and You’re Out” sentencing law;
  • laws adopted in many states to increase minimum sentences for various crimes, or lengthen sentences for crimes involving guns.

For the last two, I obtained the data and computer code for the relevant studies and analyzed them afresh.

Incapacitation: How Much Does Putting People Inside Prison Cut Crime Outside?

This is the third in a series of posts summarizing the Open Philanthropy review of the evidence on the impacts of incarceration on crime. The full report is available in PDF, Kindle, and ePub formats.

In my deterrence post, I explained why, in my reading, the research says that stiffer sentencing hardly deters crime in this country today.

In this post, I move from the “before” of incarceration to the “during,” what criminologists call “incapacitation.” Does putting more people in prison markedly reduce crime outside prison walls—at least while those people are still in prison? I think that in writing my full report, I approached the research on this question with just as much skepticism as I did with deterrence. Yet the incapacitation research better withstood my scrutiny. I am convinced that decarceration on the scale proponents hope for measurably increases crime in the short run. (It may do the opposite in the long run, by reducing exposure to the potentially criminogenic influences of prison; my next post investigates that possibility.)

I found six studies that met my criterion of exploiting an experiment or a strong natural experiment. One takes place in Italy, one in the Netherlands, and the rest in the United States. I will briefly describe four, and say more about the two U.S. ones whose data and code availability allowed for replication and reanalysis.

Aftereffects: In the U.S., Evidence Says Doing More Time Typically Leads to More Crime After

This is the fourth in a series of posts summarizing the Open Philanthropy review of the evidence on the impacts of incarceration on crime. The full report is available in PDF, Kindle, and ePub formats.

The two other in-depth posts in this series share what I learned about the incarceration’s “before” effect, deterrence of crime, and the “during” effect, which is called “incapacitation.” In sum, in the current U.S. policy context, I doubt deterrence and believe in incapacitation.

Going by the analysis so far, rolling back mass incarceration would increase crime. But that tally is incomplete. This post turns to the “after” effects of crime, which I call, cleverly, “aftereffects.” Unlike deterrence and incapacitation, even the overall sign of aftereffects cannot be determined from general principles. Having been in jail or prison could “rehabilitate” you or “harden” you into greater criminality.

The traditionally favored term for aftereffects, “specific deterrence,” captures the idea that doing time viscerally strengthens the fear of punishment and deters people from reoffending. The corrections system corrects. Penitentiaries elicit penitence. No doubt, those things do often happen. And prisons do good in other ways. Some help people off of addictive substances, teach job and life skills, or improve literacy and self-control.

However, the prison experience can also manufacture criminality. It can alienate people from society, giving them less psychological stake in its rules. It can make people better criminals by bringing them together to learn from each other. It can strengthen their allegiances to gangs whose reach extends into prisons. While some may get drug treatment, others may not, even as they suffer through withdrawal or preserve access to drugs. And incarceration can permanently mark people in the eyes of employers, making it hard to find legal work.

My review includes 15 aftereffects studies. Six conclude that more time (or time in harsher conditions) leads to less crime, eight that it leads to more crime. One study is neutral, but it involves sentences of only a day or two, for drunk driving. If we give each study one vote, then the view that prison generally increases criminality wins, narrowly. Of course, all the studies could be correct for their setting, since the prison experience varies from place to place. Bearing in mind the potential for diversity, it is still worth searching for a consensus view, as the basis for a first-order generalization about the likely impacts of decarceration nationwide. In fact, I think closer inspection of the literature tends to strengthen the view that in the U.S. today, aftereffects are typically harmful. Some reasons:

  • Of the six studies in the minority, two come from Georgia; their results appear explicable by a statistical artifact I have christened “parole bias.”
  • Another is set in California nearly a half century ago, before retribution overturned rehabilitation as the dominant philosophy of corrections in the U.S.
  • A study set in contemporary Seattle appears to suffer from baseline imbalance, meaning that the treatment and control groups differed from beginning.
  • One study in the minority looks compelling, yet is set in Norway, which appears to be much more committed to rehabilitating inmates than most American prisons (see this, this).

(The sixth looks at the impact of up to a month’s detention on juvenile offenders in Washington state. I find no serious problems with it.)

I also discovered reasons to doubt some of the studies in the majority. For example, I noticed baseline imbalance in a randomized trial that put some inmates in higher-security prison. And in the study I’ll detail next, the quasi-experiment looks imperfect.

Nevertheless a substantial family of studies coalesces around the finding that when incapacitation and aftereffects are measured in the same setting, the first is offset by the second, over time. That is to say: putting someone in prison cuts crime in the short run but increases it in the long run, on net.

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