Arizona's private prisons are not cost-effective for taxpayers and are more difficult to monitor than state prisons, according to a new report by a prison watchdog group that is calling for a moratorium on any new private prisons in the state.

The report examined the five prisons that have contracts to house Arizona prisoners and six private prisons that house federal detainees or inmates from other states, including California and Hawaii.

'Republic' special report: The Price of Prisons

Based on public-information requests and other data, the report by the American Friends Service Committee, a Quaker group that works on criminal-justice reform, concluded that:

Arizona paid $10 million more for private prison beds between 2008 and 2010 than it would have for equivalent state beds.

Arizona's pending plan to contract for another 2,000 private-prison beds would cost taxpayers at least $38.7 million a year, at least $6 million a year more than incarcerating those inmates in state prisons. Plans to add 500 more maximum-security beds in state prisons would add almost $10 million a year to the bill. The report questioned whether those beds are needed, since the state's prison population has declined over the past two years by more than 900 inmates, to 39,854 as of Wednesday.

In the past three years, private prisons in Arizona have experienced at least 28 riots and more than 200 other "disturbances" involving as many as 50 prisoners. Many of these incidents had not previously been reported to the public.

State law doesn't require the six private prisons that hold federal detainees and prisoners from other states to inform state or local authorities in the event of an escape, a riot or other disturbance, or a death in custody. The American Friends Service Committee called for requiring all private prisons to disclose the same information as state prisons.

The report criticized a recent biennial study by the Arizona Department of Corrections that found that the quality and cost of private prisons compared favorably with those of state prisons. The committee noted that the Corrections Department study didn't include data about scores of security flaws found at some prisons after three inmates escaped in 2010 from the private Kingman prison; that the study didn't look at recidivism rates, deaths in custody, suicides or homicides; and that it downplayed the fact that private prisons had consistently higher turnover and staff vacancy rates and higher levels of inmate disciplinary reports.

Corrections officials previously had said inexperienced staff may have been a factor in the escapes from Kingman and in the inability of staff there to control the prison yard during a riot in May 2010. Dante Gordon, a former inmate at Kingman, said that guards there stood by and did nothing as more than 80 White inmates attacked and beat 25 Black inmates during that riot.

The report pointed out that reports every year since 2005 by the Corrections Department, along with others by the state's auditor general, concluded that private-prison beds on average have been more expensive; but that the most recent Corrections Department study changed the way it calculated expenses to include a "range" that it termed comparable.

The report also noted that lawmakers exempted two private prisons -- the Central Arizona Correctional Facility, run by GEO Group Inc., and the Cerbat unit at the Kingman prison, operated by Management and Training Corp. -- from state laws requiring private prisons to provide an equivalent or higher level of quality than the state.

"The state has deliberately obscured information that would cast private prisons in a negative light," wrote Caroline Isaacs, the author of the report and the Friends Committee program director in Tucson.

Corrections Department spokesman Bill Lamoreaux said the director, Charles Ryan, had not had sufficient time to review the report to reply to the issues raised.

"This is stale information peddled by familiar critics," said Steve Owen, spokesman for Corrections Corp. of America, which operates the six private prisons that are not under state jurisdiction. Many of the riots and disturbances took place at those six prisons, according to data the Friends Committee reported it had been provided by correctional officials from California, Washington and Hawaii. The committee also gleaned information from lawsuits filed against CCA by Hawaiian inmates.

Without responding to specific issues raised by the report, Owen said, "the safety and security of our facilities is of critical importance to us, and we take seriously the lives of the inmates and detainees entrusted to our care."

In response to questions during a press conference at the state Capitol on Wednesday, Isaacs said it had been difficult to obtain information about prison operations.

"The fact that this information is so difficult to obtain should give Arizona taxpayers pause about the lack of transparency and lack of accountability of private prisons," she said. Her group is calling for legislation to require stricter state oversight and reporting requirements for private prisons operating in Arizona. House Minority Leader Rep. Chad Campbell, D-Phoenix, said he has introduced six bills calling for better oversight and reporting, though he doesn't expect any of his bills to get a hearing.