In her introductory comments to John Brennan's confirmation hearing to becoming director of central intelligence, Sen. Dianne Feinstein asserted that civilian casualties from U.S. drone strikes now number in the single digits annually. Those numbers are difficult to know with any certainty, and official U.S. estimates are secret. But some organizations do follow open-source reports on the strikes and attempt to track individual civilian casualties. At least some of their numbers, gathered by the scholar Micah Zenko for a Council on Foreign Relations report, appear to contradict Feinstein's assessment.

According to data from the Web site Long War Journal, U.S. drone strikes in Pakistan and Yemen killed a combined 31 civilians in 2008, 84 in 2009, 20 in 2010, 30 in 2011  and 39 in 2012.

The New America Foundation, a Washington think tank, says that U.S. drone strikes in Pakistan alone killed at least 25 civilians in 2008, 25 again in 2009, 14 in 2010, six in 2011 and five in 2012.

The U.S. also maintains drone bases in West and East Africa and conducts drone strikes in Afghanistan and Somalia, so it's plausible that the civilian casualties would be even higher than the Long War Journal and New America Foundation stats reflect.

This doesn't mean that Feinstein's numbers are necessarily wrong, of course. It's worth noting that she raised the number in the first place to argue that the U.S. government should provide greater public transparency about its drone program.

This post also appears at The Washington Post's live-blog on Brennan's confirmation hearing, with contributions from the politics and national security teams. Check it out.