Donald Trump’s Department of Justice has reopened its doors to business from private prisons. On Thursday, Attorney General Jeff Sessions made it public that he rescinded a guidance that tasked the Justice Department with ending its use of privately operated prisons.

Last year’s memo by Deputy Attorney General Sally Yates came after the Justice Department’s Office of Inspector General (OIG) found serious problems and more frequent reports of violence at privately run, for-profit facilities compared with federal public prisons.

In total, the Justice Department’s Bureau of Prisons (BOP) was to stop contracting with private operators at around a dozen prisons — although the terminations were set to take years as the federal agency let existing contracts expire instead of ending them prematurely.

The private BOP facilities don’t make up a big part of all the prisons in America or even a big segment of private prisons overseen by the federal government. There are thousands of prisons, including local jails and state prisons, all across the country — 122 of which are run by the Bureau of Prisons. And even with this announcement, other federal agencies would continue to rely on private prisons, particularly the 100-plus immigrant detention facilities overseen by the US Department of Homeland Security but run mostly by for-profit private companies.

Still, the decision is sure to upset liberals, many of whom blame private prisons for perpetuating mass incarceration. But it will likely come as welcome news to conservatives, who see private prisons as a cheaper alternative to public ones — even as the data suggests that private facilities may be more dangerous.

What OIG’s investigation into private prisons found

Generally, privately run federal prisons — known as “contract prisons” — house low-security inmates, typically undocumented male immigrants. So the comparisons in the 2016 OIG report weren’t to high-security facilities, but to other low-security prisons run by the US Bureau of Prisons (BOP).

“We found that in a majority of the categories we examined, contract prisons incurred more safety and security incidents per capita than comparable BOP institutions,” the report concluded, based on its analysis of 14 private prisons and 14 public prisons from fiscal years 2011 to 2014.

OIG found problems in six categories: contraband, reports of incidents, lockdowns, inmate discipline, telephone monitoring, and selected grievances. Private prisons reportedly had fewer positive drug tests and reported incidents of sexual misconduct.

“For example, the contract prisons confiscated eight times as many contraband cell phones annually on average as the BOP institutions,” the report found. “Contract prisons also had higher rates of assaults, both by inmates on other inmates and by inmates on staff.”

Privately run facilities also consistently put inmates in solitary confinement units just because they didn’t have enough room to put them with the general population — a violation of federal rules for solitary. And the private prisons appeared to provide inadequate medical care to inmates.

The report had a big limitation: It couldn’t examine all the factors that contributed to these differences, including the effects of inmate demographics and facility locations. And some of the numbers could be misleading; for example, maybe inmates were more willing to report sexual misconduct in public facilities, which suggests that public facilities could be better at handling sexual misconduct even if they have more reports of it.

But the findings were bad enough that OIG recommended the federal government take more serious actions to oversee privately run prisons. And the BOP responded with swift force, with plans to cancel contracts on its remaining 13 private facilities.

Private prisons aren’t a big part of the US prison system, but they have problems where they exist

Privately run prisons are a sizable part of America’s prison system, but not even close to a majority. They hold about 18 percent of federal prisoners and 7 percent of state prisoners, according to the American Civil Liberties Union. (More than 87 percent of all prisoners in America are in state facilities.)

As I’ve written before, this shows that private prisons aren’t really the drivers of mass incarceration — a popular belief held by liberals — but instead a response to it: Once public prisons got too crowded, legislators around the country began to seek out less expensive options to take in some of the new prisoners. So private prisons began holding inmates on the margins.

Still, where private prisons do exist, they seem to pose extraordinary problems.

The OIG report isn’t the first to indicate that private prisons are worse off, although it’s the most recent one. A 2001 report from the Department of Justice found the rate of inmate-on-inmate violence at private prisons was 38 percent higher than the rate at public prisons. And in a four-month undercover investigation, reporter Shane Bauer witnessed high levels of violence — particularly stabbings, which seemingly went underreported in official numbers — and lockdowns at a private prison in Louisiana.

The problems in private facilities generally follow the same theme: They seem to have big problems staffing up, because private prisons’ for-profit motive incentivizes the facilities to keep salaries and staff numbers low. As a result, the limited number of guards can’t handle, deter, or stop outbreaks of violence as effectively as a bigger staff in, say, a public prison can. And even though state and federal governments are supposed to oversee these prisons, it’s harder to do that indirectly through a private contractor than directly through your own publicly hired and managed staff.

This doesn’t mean public prisons are pristine. There are plenty of terrible stories from public facilities, such as Pelican Bay in California and Rikers Island in New York City. Last year, I reported on a transgender inmate’s horrific experience through multiple public prisons, where she was repeatedly sexually assaulted and brutalized as public prison officials did little about it.

But based on the available data, it does seem private prisons are even worse.

Proponents of private prisons argue that they can save money, since private companies can run them more efficiently. The OIG report cautions against that conclusion, given the problems that come with private prisons. But even if the claim is true, the savings may not be worth the extra dangers that come to staff and inmates at private prisons. As Yates noted in her memo, “Bottom line, I’d also say, you get what you pay for.”

Sessions, apparently, disagrees.

Watch: How mandatory minimums helped drive mass incarceration