Facebook knows a lot about how it affects its users, because it’s investigated possible negative impacts. For instance, internal research showed that one of its algorithms actually encourages angrier content. Or that Instagram, which it owns, makes body image issues worse for teen girls. And even though it knows all this, it doesn’t share the information, either with Congress or its own oversight board. That’s the finding of an investigation out this week from The Wall Street Journal, called the Facebook Files. It’s a topic for "Quality Assurance." Marketplace's Jed Kim speaks with Jeff Horwitz, a reporter for the Journal and an author of the series.