According to the Marshall Project, between 2000 and 2014, the average time served rose by around 37 percent.
And the 10 percent who have been in prison for the longest period, mostly serving sentences for violent crimes, saw their jail time by go up by 42 percent.
Adam Gelb, director of the Public Safety Performance Project at The Pew Charitable Trusts, told the Marshall Project, the numbers didn't surprise him and that he sees them as proof of a system gone awry.
“There is little to no evidence that longer prison terms produce safety,” Gelb said. “If the objective is punishment for the sake of punishment, regardless of whether we are safer, then the present system is successful.”
The study based its findings on data collected between 2000 and 2014.
It found that in order to reduce the number of people incarcerated in the U.S., currently standing at 2.2 million people, the criminal justice system will have to look at how people who commit violent crimes are treated.
“You could take every nonviolent offender out of prison today. We would still have mass incarceration,” Michael Jacobson, director of the CUNY Institute for State and Local Governance told the Marshall Project. “Targeting low-level offenders is necessary, but it cannot resolve the prison population problem by itself.”
The data also showed racial disparities among the population serving long-term prison sentences.
According to the report, four out of every 10 people in jail are Black.
And the number rises to almost five Black prisoners out of every 10 for those serving the top 10 percent of long term sentences.
Another study "Color of Justice: Racial and Ethnic Disparity," confirmed the disparity stating, "Black people are incarcerated at a rate over five times that of white people nationwide (and significantly higher in many states).
The Urban Institute study collated the data from the National Corrections Reporting Program, NCRP, available from 44 states and Washington D.C.
It also found that close to two out of five of those serving the longest terms were sentenced while they were under 25.
In Michigan, for example, those who have been in prison the longest—the top 10 percent—had served an average of 10 years in 1989.
By 2013, the longest-serving prisoners had been incarcerated for 26 years.
A number of nonprofits working for criminal justice reform, like the ACLU, Rebuild the Dream, and Just Leadership USA, are working on ways to reduce the prison population by 50 percent over the next 10 to 15 years.