We have a grand social experiment on incarceration and the consequences for crime to our south, in the United States of America. You will know that the United States is now the largest incarcerator in the world; that one out of every four persons in the entire world—that is, on the planet—who are in prison is in a prison in the United States. Approximately 1% of the American population is under some form of judicial supervision. It has been a catastrophically expensive exercise, but it has not produced the reduction in crime rates that you would expect for that rate of incarceration.
So the evidence from the United States and the evidence from the U.K. is that growing the rate of incarceration does not reduce the rate of crime. In fact, there is emerging evidence, again coming from the United States and the U.K., that growing the rate of incarceration may actually increase the rate of crime because of what's called “prisonization”, or the experience of incarceration and the difficulty thereafter of successful reintegration. There is a large body of evidence, and I'm happy to supply it to you—some of it is referenced in this paper—that simply growing the rate of incarceration does not reduce crime.