Well, the basic idea is that a government prison would have the goals of society in mind (both security and rehabilitation) whereas a private prison's profit motive benefits most from having as many prisoners as they can get for as long as possible.
Actual rehab runs contrary to that; facilitating a state of affairs that results in more prisoners (repeat and new) for longer periods is going to be a primary goal.
What solutions are there that aren't simply large carrots (bonus' for prisons when repeat offense rates fall?) or large sticks (penalties/fines for the opposite)?
Agreed that that's the basic idea behind government-run anything -- its ostensible adherence to the benefit of society. But that's the naivete I was referring to: in the end there is no "government" per se, just a bunch of self-interested individuals. They all stand to benefit from overemphasizing a need for their department, bigger budgets, better benefits, tenure, and the political clout to influence those things.
There will always be undesirable incentives. Say we reverse things and pay the company more for reformed prisoners who make parole earlier. Now the incentive is to err on the side of leniency and potentially release more dangerous criminals earlier. You might then counteract it by penalizing the company even more if one of their parolees ends up back in the tank within X period of time; that might help, but depending on the parameters it could make them so gun-shy that we're back where we started -- holding people for longer -- but with a more complex system with more opportunity for schemes and loopholes.
It's not an easy problem by any means. As I said, I want to find some studies; I'm open to what the results show, but I'm very wary of trusting government simply because their purported goal is social benefit.
Actual rehab runs contrary to that; facilitating a state of affairs that results in more prisoners (repeat and new) for longer periods is going to be a primary goal.
What solutions are there that aren't simply large carrots (bonus' for prisons when repeat offense rates fall?) or large sticks (penalties/fines for the opposite)?