"As we refine our approaches, we’ll start distinguishing more and more between different types of content," Backstrom says. "But, for right now, when we think about how we identify 'high quality,' it’s mostly at the source level."

Backstrom declined to say specifically which sources Facebook has deemed low quality or high quality, but that designation is based in part on comments, clicks from mobile users, and user surveys.

"Our goal is to provide user value," he says. "We’re trying to do that algorithmically, and if people find ways to game the algorithms that we have, then we have to adapt."