The first private prison in the United States opened in 1984 amidst the war on drugs and overcrowding in public prisons. Now a multi-billion dollar industry, private prisons incarcerate about 8 percent of all America's inmates.

In a paper in the American Economic Journal: Economic Policy, University of Wisconsin-Madison economist Anita Mukherjee examined the impact of private prisons on the length of time that inmates serve.

She found that inmates in Mississippi served an average of 90 extra days if they were sent to a private facility. The results undercut the industry's claims that private companies provide correctional services more efficiently and at lower cost to governments.

Professor Mukherjee recently spoke with the AEA's Tyler Smith about why private prisons tend to hold inmates longer and how private prison contracting could be reformed.