According to Facebook’s guidelines, a team of news editors are instructed on how to ‘inject’ stories into the trending topics module. Photograph: Adam Berry/Getty Images
Leaked documents show how Facebook, now the biggest news distributor on the planet, relies on old-fashioned news values on top of its algorithms to determine what the hottest stories will be for the 1 billion people who visit the social network every day.

The documents, given to the Guardian, come amid growing concerns over how Facebook decides what is news for its users. This week the company was accused of an editorial bias against conservative news organizations, prompting calls for a congressional inquiry from the US Senate commerce committee chair, John Thune.

The boilerplate about its news operations provided to customers by the company suggests that much of its news gathering is determined by machines: “The topics you see are based on a number of factors including engagement, timeliness, Pages you’ve liked and your location,” says a page devoted to the question “How does Facebook determine what topics are trending?”