“The study found that sentencing someone to prison had no effect on their chances of being convicted of a violent crime within five years of being released from prison. This means that prison has no preventative effect on violence in the long term among people who might have been sentenced to probation. It also found a preventative “incapacitation” effect in the short term, during the time when prisoners were still in prison, but this effect is smaller than we typically assume. Preventing one person who was previously convicted of a violent crime from committing a new violent crime within five years of their sentence requires imprisoning 16 such individuals.”

More about Morenoff co-authored study on the effect of imprisonment discussed in Scientific American >