Back in April, a Pentagon study, first leaked to the New York Times, claimed that 14 percent of the more than 540 detainees released from the Guantanamo Bay detention center were confirmed or suspected of "reengagingng in terrorist activities." The study provided fuel for the ongoing debate over President Barack Obama's plans to close GTMO, as it's known, by next January, as well as the larger fight over his and his predecessor's national security policies.

The Pentagon report, based on information from the Defense Intelligence Agency, came in for some immediate criticism, not least because it assumed that every individual detained at Guantanamo was a terrorist in the first place. An exhaustive McClatchy series last year found that some of the men detained at Guantanamo did not belong there, while others were radicalized by conditions at the facility.

(The Times acknowledged errors in the way it handled the story in an editors' note).

Now comes a new analysis by the New America Foundation, a centrist think tank, that also challenges the Pentagon assessment. Analysts Peter Bergen and Katherine Tiedemann put the actual recidivist at about one in 25, or 4 percent. They define recidivism as those who are confirmed or suspected to be involved in anti-U.S. violence, and base their study on Pentagon reports, news studies and other public records.

The New America Foundation report found 21 individuals who engaged or may have engaged in anti-U.S. or insurgent activities after release from GTMO. (The Pentagon study found 27 confirmed and 47 suspected recidivists, although 45 of them were not named to protect intelligence sources and methods, according to Navy Cmdr. J.D. Gordon, a Pentagon spokesman).

Gordon said Monday, "We stand by the analysis that approximately 14 percent of the ex-Guantanamo detainees are confirmed or suspected of having returned to terrorism."

One difference in the analyses is that the New America Foundation study excluded former detainees who may have engaged in political violence, but not against U.S. interests, such as two men convicted in 2006 of blowing up a Russian gas pipeline. Even if this group is included, the recidivism rate if about 7.5 percent, not 14 percent, the report states.

Spokesman Gordon, meanwhile, rejected the proposition that some of the detainees may not have been terrorists when they went into Guantanamo, but were by the time they left. "Our views is that all the detainees who went to Guantanamo were enemy combatants," he said, noting that formal review panels have found that 38 of the approximately 540 released were "no longer enemy combatants." None of those, he said, were included in the Pentagon's list of 74 recidivists.