Private prisons have become more popular, but they have not made corrections cheaper or safer, according to a new report examining the growth of private prisons in the U.S. between 1999 and 2010. 

The number federal prisoners in private prisons increased 784 percent, found The Sentencing Project, a Washington D.C.-based criminal justice research and advocacy nonprofit. The increase reached 40 percent at the state level. While privatization may offer savings, the research found, it often comes at "the detriment of services provided." 

Too Good to be True: Private Prisons in America also examines how politics, including heavy lobbying by private companies, influenced the expansion. 

Read the full report here.