The study adds new evidence to the argument that a key driver of high incarceration rates is the readmission to prison of individuals recently released from prison, a phenomenon that has been called prison's "revolving door." It also shows that this self-perpetuating cycle of prison admissions is being driven largely by readmissions to prison for technical violations of parole rather than new crimes.
The study, conducted by a research team at the U-M Institute for Social Research, including Jeffrey Morenoff, director of the U-M Population Studies Center and David Harding, professor of sociology at the University of California-Berkeley, collected data on all individuals sentenced for a felony in Michigan between 2003 and 2006, about 111,110 people. The researchers compared prison readmissions and felony convictions, called recidivism, of those sentenced to prison versus probation.
The researchers found that people convicted of felonies who were sentenced to prison rather than probation had almost a 20-percent higher chance of being returned to prison within five years, compared to someone who was sentenced to probation.
Probation is a punishment given to people convicted of felonies in place of prison time. Parole is a release from prison. In both, the individuals are under strict supervision, but post-prison supervision tends to be much more stringent, the researchers say. In fact, technical violations of parole account for almost 30 percent of all prison admissions nationwide.
"Lots of people talk about a revolving door between prison and the community, but the causal story behind this metaphor has been difficult to test," said Morenoff, who is also a professor of sociology and public policy. "Our study provides some of the strongest evidence yet that being sentenced to prison increases the chances that someone convicted of a felony will recidivate, and it shows that the main force that sets the revolving door in motion is the likelihood of being sent back to prison for a technical violation of parole."
The study compared people sentenced to prison and probation on multiple indicators of recidivism, including future prison admissions and felony convictions. The researchers found that returns to prison for technical violations of parole were the primary reason why people who were sentenced to prison at the beginning of the study period were more likely than those given probation to experience a subsequent prison spell. Being sentenced to prison versus probation had no significant effect on the likelihood of being convicted of a future felony.
The findings suggest that parole supervision after prison, which the researchers argue is generally more stringent than probation supervision, increases imprisonment through the detection and punishment of low-level offending or violation behavior. This kind of behavior would not otherwise result in imprisonment for someone who had not already been to prison or who was not on parole.
The results demonstrate that the revolving door of prison is in part an effect of the nature of post-prison supervision, Morenoff and Harding say.
In Michigan, people charged with felony offenses are randomly assigned to a judge. This randomness allowed the researchers to conduct a natural experiment in which they took advantage of the different ways randomly assigned judges would sentence those convicted of felonies in order to approximate the conditions of a controlled experiment in which people convicted of felony offenses would be randomly assigned to either prison or probation.
"The main hypothesis we set out to test was whether incarceration was a deterrent against crime, and it's not—at least not by this study," Morenoff said. "It puts people away, and when they're incapacitated, it prevents them from committing common crime, but once a person is released from prison, they are at higher risk for being returned to prison."
Failure of individuals to report to their parole officers was cited in 73 percent of violation reports, while failure to complete required program was reported in 61 percent of cases, substance abuse in 50 percent of cases, moving residence without permission including absconding at 50 percent, curfew violation or entering restricted areas at 49 percent, associating with felons at 29 percent, and possession of weapons other than firearms at 29 percent.
"In this political climate, in which we see more interest in returning to some of the more punitive policies that our country was trying to move away from in order to reduce mass incarceration, this is one caution that those policies could increase the size of our prison population without measurable gains in public safety," Morenoff said. "Prison growth is partially a self-perpetuating cycle."