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Why prisoners may be less likely to reoffend than you think

One of the most common criticisms of US prisons may be totally wrong.

If you look at conventional prison statistics, you might get the idea that most inmates eventually end up back in prison. A 2011 report from the Pew Center on the States, for instance, characterized the criminal justice system as "the revolving door of America's prisons," finding that nearly half of inmates go back to prison. Other statistics suggest that a majority of prisoners will reoffend within three years of their release.

But a recent report by economist William Rhodes suggests these numbers are wrong — and, in fact, two in three ex-inmates won't return to prison, and only 11 percent will go back to prison more than once after their initial release.

Why are the commonly cited statistics potentially misleading? Rhodes draws on an analogy to explain that previous estimates overrepresent the rate of inmates who return to prison:

When performing mall intercept surveys, researchers randomly sample shoppers who appear in the mall during the period when the survey is administered and ask respondents questions such as: How frequently do you visit a mall? Obviously, frequent mall visitors are overrepresented in intercept surveys, so when they analyze survey data, statisticians weight the data to correctly represent all mall visitors.

Offenders who repeatedly return to prison are like frequent mall visitors – they are overrepresented in samples used to estimate the rate at which offenders return to prison. If a statistician fails to weight his statistics to correct for this overrepresentation, offenders will appear to be highly recidivistic: One of every two will return to prison within five years. If the statistician correctly weights her statistics, offenders appear less recidivistic: Two of every three will never return.

Getting these figures right is critical to understanding why criminal justice reform, which by and large aims to reduce America's enormous prison population, won't significantly endanger the public.

If most prisoners reoffend, then letting out a bunch of inmates — or reducing their prison sentences — is a seriously scary idea. Could we really justify such an approach, especially to just save money on prison costs? The New York Times, for one, warned of scenario in a recent piece about an alleged cop killer who was reportedly "given a string of breaks" by the criminal justice system.

But if most prisoners don't reoffend, and even more don't reoffend more than once, then reform suddenly seems a lot more sensible. After all, why keep people in prison when they're very likely no longer a public threat? Especially since the US already leads the world in incarceration, that just seems wasteful.

Rhodes's analysis suggests that the latter scenario — in which most people don't reoffend — is right. And there's other evidence to support this point: A growing body of research shows that people essentially age out of crime, since they're a lot more likely to act out as youths. So there's a good chance somebody will be much less likely to reoffend after a few years in prison through a natural process of maturation. And all of that suggests we can safely let a lot of prisoners free without huge concerns for public safety.

(Still, reform will always involve risks — even a 33 percent recidivism rate means one in three inmates are being let out of prison and committing more crimes, and we'll likely never get that rate down to zero even through big reforms. So as Vox's Dara Lind explained, accepting the risk of some ex-inmates reoffending is a necessary step toward ending mass incarceration.)

But if the public and lawmakers aren't made aware of the actual figures and research, or are misled with improperly vetted and exaggerated numbers, the conversation is always going to be skewed toward more and more incarceration. That's why getting these numbers right is important.