The NSA could figure out how many Americans it’s spying on. It just doesn’t want to.

[Commentary] Documents released by whistleblower Edward Snowden reveal that the information includes some data about the locations of Americans, but didn't provide specific estimates about how many Americans were affected. When asked about it, a National Security Agency spokeswoman claimed it would be impossible to come up with an estimate. This seems difficult to believe.

The metadata the NSA collects about mobile devices should contain more than enough information to make an educated guess about whether they are associated with an American. By examining a random sample of devices it is tracking, the agency should be able to come up with a reasonable estimate of how many of those devices are associated with a US person. That doesn't translate to a precise count of the number of Americans subject to surveillance. Some Americans own multiple cellphones, and some foreigners might sign up for US cellphone plans. But it should give at least a rough estimate of how many Americans are having their location data scooped up by the NSA.