STEVE INSKEEP, BYLINE: New research explores the influence of private prisons in the United States. Convicted criminals in some states may end up in a facility run by a private company, which is a big change from past generations. And that has prompted researchers to ask, does the existence of private prisons change other parts of the criminal justice system? In particular, does it influence the sentences handed out by judges? NPR's social science correspondent Shankar Vedantam is here to explore that.
SHANKAR VEDANTAM, BYLINE: Hi, Steve.
INSKEEP: So do the prisons somehow influence judges?
VEDANTAM: The short answer is yes. I was speaking with Christian Dippel. He's an economist at UCLA. Along with Michael Poyker, he analyzed data from 13 states, including Texas, Arkansas, Virginia, Tennessee, Kentucky and North Carolina. Now, lots of things could drive sentencing length. To analyze the effect of private prisons, Dippel compared adjoining counties in different states. Some states saw increases in private prisons. Others did not. Looking at similar crimes and defendants, Dippel says private prisons did have an effect on the length of sentences.
CHRISTIAN DIPPEL: When a private prison opens in a state, then the average length of a sentence increases by 23 days. The presence of a private prison does not make it more likely that you go to prison. But it makes it - makes your average sentence length 23 days longer.
INSKEEP: Wow, and these are people right on either side of a state line but in a somewhat different system. When you tell me this, Shankar, my mind goes to a kind of cynical place. It makes me wonder, are these for-profit companies somehow lobbying judges to give people longer sentences?
VEDANTAM: I think that was one of the concerns that motivated the study, Steve. Private prisons do lobby state legislators. And there have been some egregious examples of prisons actually paying judges to hand out harsher sentences. But the researchers think the data here are more consistent with a different explanation. States can mandate how much private prisons can charge. And the data suggest the longest sentences are handed down in states where private prisons offer the largest cost savings. Dippel thinks that judges might be influenced by such concerns.
DIPPEL: I would levy a certain sentence, but I'm aware of the fact that that's expensive. Or I'm aware of the fact that we are suffering from capacity constraints in our prison system. So I'm going to reduce the sentence by a little bit. And when that - when that constraint relaxes, then I'm going to increase the sentence by a little bit.
INSKEEP: Wow, so the difference in cost between one state and another for imprisoning somebody might influence the judge to change the sentence. Is there evidence, though, that private prisons are actually increasing the number of people in prison in America - not more people being convicted, but those convicted staying there longer?
VEDANTAM: Now, it's possible that's playing some role, Steve. But Dippel thinks that the overall size of the U.S. prison population is likely driven much more by policies, such as the war on drugs. It's also worth mentioning that this study, like others, finds racial disparities. Blacks are likely to get harsher sentences for committing the same crimes. I think the big message of the study is that practical concerns matter when it comes to the criminal justice system. Everything is not just about ideological differences.
INSKEEP: Shankar, thanks.
VEDANTAM: Thank you, Steve.
INSKEEP: NPR's Shankar Vedantam joins us regularly to talk about social science research. And you can listen to more of his work on the podcast that he hosts, which is called Hidden Brain. Transcript provided by NPR, Copyright NPR.