The details of Mr. Kavaja's life are difficult to verify and often clouded by his boasts.
The accounts of the extremists — generally militant Islamists — are difficult to verify.
The government's figures for job creation or preservation are difficult to verify.
Much of what is known about Gadahn's activities in Pakistan comes from intelligence reports that are difficult to verify.
Essential genes of pathogens are potential therapeutic targets, but are difficult to verify.
As a result, estimates of dead militants are difficult to verify, according to three military officers familiar with the process.
Some details could not be confirmed, and numbers, typically inflated by both sides, are difficult to verify.
Such videos are difficult to verify, but the episode on Wednesday seemed to be confirmed by other witnesses.
Reports of the fighting are difficult to verify; the government has barred most journalists and aid workers from the conflict zone.
Independent reporters and most humanitarian groups have been barred from the battle zone, and reports from the area are difficult to verify.
Independent reports about North Korea are difficult to verify and the country is culturally isolated, leaving speculation and humour to fill the void.
