Today in the U. S. about 9 percent of those behind bars in 28 states and in federal prisons — more than 128,000 people — are in prisons run by the private sector. But private prisons have turned out to be neither better nor cheaper. They have about the same recidivism rates as their government-run counterparts — nearly 40 percent -- and there is no evidence that private prisons are more cost-effective than public prisons. In a new experiment, Australia and New Zealand contract with private companies to design and manage facilities and reward the companies financially if their prisoners’ recidivism rates fall.