Q:

Do private prisons have 49% more inmate-on-staff attacks than publically run prisons?

Peter Wagner writes in Section III: The Prison Economy:

Percent more inmate-on-staff assaults in privately run medium and minimum security prisons than in publicly run facilities: 49%

Is that data accurate? Is it based on a comparison of similar prisoners?

A:

Data for US prisons is accurate based on comparison with other public run prison facilities which is listed below. 
The figure of 49% inmate-on-staff assaults in privately run medium and minimum security prisons than in publicly run facilities is mentioned in a written testimony for a 2007 Texas Senate Criminal Justice Committee.

Written testimony before a 2007 Texas Senate Criminal Justice Committee reported 49% more inmate-on-staff assaults and 65% greater inmate-on-inmate assaults in private minimum and medium security facilities than in comparable publicly run facilities.

James Austin's survey of the prison industry in 1997 
also mentions the figure of 49% more inmate on staff assaults in private minimum and medium security facilities than in comparable publicly run facilities.

An industry-wide survey conducted in 1997 by James Austin,
  a professor at George Washington University, found 49 percent more
  inmate-on-staff assaults and 65 percent more inmate-on-inmate assaults in medium- and minimum-security private facilities than in medium- and minimum-security prisons run by government.

The number of assaults on staff is noted to be increased in state and federal prisons from 1995 to 2000 and the size of the increase was greatest for private institutions. The rate of assault on staff in confinement facilities
under Federal or State authority is noted to be nearly the same which was 14.7 per 1,000 inmates in 1995 and 14.6 per 1,000 in 2000.  

Stephan and Karberg (2003) found, using data collected from correctional institutions around the United States, that the number of assaults on staff and inmates increased in state and federal prisons from 1995 to 2000 and
  that the size of the increase was greatest for private institutions.

Curtis R. Blakely and Vic W. Bomphus in 2004 have reported that in private prisons, there was almost 50 percent more inmate on staff assaults.

A 2004 report by the Federal Probation Journal that specifically controlled for prison security level found that private prisons had 50 percent more inmate on inmate assaults and almost 50 percent more inmate on staff assaults.

The figure of 49% inmate-on-staff assaults in privately run medium and minimum security prisons than in publicly run facilities is present here. The significantly higher rate of assaults on staff and
inmates in private prisons is also confirmed through national survey results present here.

The Bureau of Justice Assistance reported that private prisons experienced 49% more assaults on staff and 65% more inmate-to-inmate assaults than public prisons.

Rates of violence between inmates and staff may be higher at private prisons than government facilities.

An independent state commission in Ohio recently found that rates of violence soared after it sold a state prison to a private company. Audits of the facility following the sale revealed that violence among inmates and between inmates and staff increased significantly under private control.

This phenomenon is different from that of the United Kingdom where private prisons outperform the government prisons in several performance indicators except for assault between inmates.  

