ED FELTEN ON NSA SNOOPING: 51% foreign test doesn’t protect Americans. “As an example, consider Facebook, which appears to have about 1 billion users worldwide, of which roughly 160 million are in the U.S and the other 840 million are foreign. If you collect data about every single Facebook user, then you are getting 84% non-U.S. records. So even a ‘collect all data’ procedure meets the 51% foreign test—despite doing nothing to shield Americans from collection.”