Monday, November 22, 2010

Prison, parenting, selection bias, and measuring success

In both parenting and the legal system one must carefully consider the role of punishment.  Recently, the discussion surrounding imprisonment has become focussed on rehabilitation, using recidivism rates inappropriately as a statistical measuring stick of success.  This seems to be the product of confusing success in parenting with success in crime prevention.

For seasoned criminals one must ask whether rehabilitation is genuinely the purpose of imprisonment.  Surely, a more effective way to rehabilitate offenders would to have a wholesome family adopt them into their home and demonstrate law abiding ways to live and prosper.  Imprisonment with other criminals for an extended period seems strongly counterproductive to a shift to a more law abiding lifestyle.

As one insightful commenter noted here, even low rates of recidivism would be not be a signal of the success of imprisonment  because they can be caused by factors other than reform or a desire ‘not to go back there.’
1.      Crime is committed mostly by young men. As a man gets older, he’s less likely to reoffend.
2.      Crime is sometimes committed as a one-off event (such as crimes of passion, or rare opportunity). These are unlikely to be repeated.
3.      Convicts are sometimes innocent. These people, too, are unlikely to reoffend

Clearly, the function of imprisonment is to act as a deterrent to all potential criminals, not just to those who have already been imprisoned. This is quite different to punishments set by parents for their children, where there purpose is twofold – prevention of initial offence of a single child (or few children), plus a deterrent to future offences, or what might be known as rehabilitation.

Recidivism rates after punishment are important for parents.  Repeat offences by children (it sounds odd to say it like that) signal that the punishment was not appropriate for either the initial prevention, or rehabilitation.  For parents to encourage appropriate behaviour in their children they need to adapt their punishments so that each child will respond to them.  There is usually no one-size-fits-all approach.

With criminals, punishment needs to be a one-size-fits-all approach, and if that is insufficient to prevent some crime, then those individuals will have to accept that punishment, often repeatedly. There is no room, unlike parenting, to adopt individual punishment regimes to rehabilitate the whole criminal populous. 

I want to leave you with a long excerpt on the inappropriate use of recidivism rates to evaluate the effectiveness of imprisonment from this article.

This is a peculiar objection to imprisonment—rather like complaining that your TV is not working because it does not defrost chickens. Reducing repeat offending is not the purpose of prison. Its purpose is to reduce offending. It does this in two ways: by deterring people from committing crimes and by positively preventing them from doing so while they are inside.

But doesn't the high recidivism rate show that prison is not an effective deterrent after all? It does not. Testing the deterrence effect of prison by observing the proportion of ex-prisoners who commit crimes is a bad case of the statistical error of "sample bias." Prisoners are, by hypothesis, people for whom the threat of prison is an insufficient deterrent to crime. That prison does not deter ex-prisoners tells us nothing about how much it deters the rest of the population, nor therefore by how much it reduces crime.

Once you think of criminal punishments as deterrents, 100% recidivism is unsurprising, because the first conviction is the most expensive for a criminal. This is when he incurs the one-off, irrecoverable costs of becoming a known criminal, such as diminished career and social prospects. If the chance of incurring these costs (in addition to the penal costs) did not deter him from committing a crime, then the inevitably lesser costs of subsequent convictions are unlikely to deter him. This is true whatever the legal penalty for crime—be it torture, prison or "community service"—and however effectively it deters first crimes. Recidivism is a red-herring.

Alas, those who complain about recidivism do not think of imprisonment as a deterrent. They think of it as being more like a medical treatment, aimed at "rehabilitating" people who have succumbed to a behavioral disease that they caught from our unhealthy society or, perhaps, from their genetic inheritance. Crimes are not the actions of people weighing costs and benefits; they are the symptoms of a condition, like the suppurating blisters of an impetigo sufferer. Criminals need to be cured, not punished.

To understand the mistake here, consider my misspent youth. I often achieved mediocre grades for my schoolwork. This would prompt my teachers to speak rudely to me, usually accusing me of being unacceptably lazy. Yet I noticed that when one of my notoriously stupid classmates achieved the same mediocre grades, praise was heaped upon him. This struck me as unfair because, as I pointed out to my teachers, I could no more help being lazy than he could help being stupid. And then they spoke rudely to me again.

Whatever the justice of it, my teachers' unequal treatment was justified. For, although we may all have dispositions that we did not choose, some of these dispositions still respond to incentives. Because I was lazy, I required more badgering than most pupils did. Nevertheless, enough badgering would make me work. We lazy people are not immune to incentives. No amount of badgering or other punishment, however, would have improved the mental powers of my stupid classmate. Because stupidity does not respond to incentives, scolding him for it would have been pointlessly cruel.

Many criminals may well have unchosen dispositions that incline them toward violence or disobedience, or that make it harder for them to find paid employment and hence incline them toward illegal sources of income. Discovering such causes of crime makes many people move into the anti-punishment camp. But it should not. Punishment would be misguided only if, like stupidity, such criminal dispositions did not respond to incentives.

Yet they obviously do. Imagine that some technological advance meant that every theft resulted in a correct arrest, and that the convicted thieves were brutally tortured. Can anyone doubt that thievery would go into sharp decline? Or, if you prefer real world examples, compare the amount of drug-related crime in the U.K., where convicted drug dealers are imprisoned, with the amount in Singapore, where they are executed.


  1. Don't suppose you have time to include drawings, cartoons or graphs on these blogs?

  2. I'm not sure what you are trying to get at other than recidivism rates being a poor metric for evaluating our justice system.

    I'm not sure of the exact sentencing provisions in QLD, but in VIC, any sentence must be for at least one of the following purposes:

    * punishment
    * deterrence
    * denunciation
    * rehabilitation
    * and community protection

    A lot of thought generally goes to tailoring the sentence for the offence and the offender and ensuring that it will be successful in achieving its aims.