If you’re a prison guard or inmate, your safety may hinge on whether you’re positioned at a privately run, for-profit prison or a public facility.

That conclusion comes from a new report by the US Department of Justice’s Office of Inspector General (OIG), which looked at federal prisons run by three companies — the Corrections Corporation of America, the GEO Group, and the Management and Training Corporation — to compare them with similar public prisons. And the findings don’t look good for private prisons.

What the federal private prison report found

Generally, privately run prisons — known as “contract prisons” — house low-security inmates, typically undocumented male immigrants. So the comparisons weren’t to high-security facilities, but 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.”

Private prisons “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 rules for solitary. And the private prisons appeared to provide inadequate medical care to inmates.

The report had a big limitation: It couldn't look at all the factors that contributed to these differences, including the effects of inmate demographics and facility locations. But the findings were bad enough that it recommended the federal government take more serious actions at overseeing privately run prisons.

Private prisons aren’t a huge part of the US prison system, but seem to 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 16 percent of federal prisoners and 6 percent of state prisoners, according to the American Civil Liberties Union. (More than 86 percent of all prisoners in America are in state facilities.)

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

The OIG report isn’t the first to indicate private prisons are worse off, although it is 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.

Based on the available data, it does seem private prisons are even worse

The problem in private facilities generally follows the same theme: They seem to have big problems staffing up, because the for-profit motive for private prisons incentivizes them 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.

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. Earlier this year, I reported on a transgender inmate’s horrific experience through multiple public prisons, where she was repeatedly sexually assaulted and brutalized.

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.