I have been reading Prisongate: The Shocking State of Britain's Prisons and the Need for Visionary Change by David Ramsbotham, the former Chief Inspector of Prisons. It's an interesting read, with thought-provoking perspectives and the purpose of prisons in society, as well as an inside view of how they work and don't work in the UK.
The book and a recent article in The Economist point to the increasing overcrowding in prisons. This seems to be the main problem, and the both the article and book point out that overcrowding is caused by (a) more offenders being sentenced to prison and (b) longer sentences. It's a classic stock and flow system:
In this diagram, the levers that society can pull (through policy decisions by theDepartment of Justice and the courts) are shown in boldface. There are three levers:
- How many offenders are sent to prison
- How long they stay
- How many prisons are built
The plumbing of this system works as follows. There is a basic level of crime (say, x crimes per each 100,000 population per year), and a certain fraction of these are sent to prison. They stay there for a certain period of time (Length of sentence in the diagram, and decided by the courts), after which they are released. They then re-enter society (into the stock marked "Ex prisoners"), but may misbehave again and get caught, and thus reenter prison.
Where it gets interesting is that there is a feedback loop caused by overcrowding. Studies have shown that cramming more people into the same number of cells, and providing fewer opportunities for exercise and education (because these resources are spread thinner as well), increases the chance that prisoners will offend again after they are released ("Recividism rate" in the diagram). So putting more people into prison, a "tough line" policy that is becoming popular with politicians and the public, could actually be making things worse.
The solution, of course, would be to increase the "Prison capacity" stock, by building more prisons, or by reducing either the fraction of convictions sent to prison or the average length of sentence, or a combination of these three levers.
This model is incomplete in that it suggests prison is a closed system, i.e., that the number of prisoners does not affect society outside of prison. This is clearly not the case. Perhaps there is some feedback between the number of ex-prisoners and the crime rate among the population that has never been to prison. And having a huge number of prisoners can't be a good thing. So reducing the crime rate is the ultimate objective. And how can that be achieved? Probably not through the justice system alone.
In a future entry, we'll build a simulation of this system, and see how much of an impact each lever has on the overall behaviour of the system.