Algorithmic selection and supply of political news on Facebook

•News algorithms affect the amount of substantive political news on Facebook.•The higher number of political news items on Facebook increases ideological concentration.•Reduction of ideological concentration operates through the “Law of Large Numbers” and a higher representation of niche ideologies. Facebook has been criticized for exposing its users to low-quality and harmful information, including fake news, hate speech, and politically one-sided content. In December 2013 and again in August 2014, the platform updated its news feed algorithm to increase user exposure to quality content of news publishers, while curbing the proliferation of non-informative posts. This paper uses a sample of German newspapers to investigate the conjecture that these modifications raised the incentives to publish quality news stories on the platform, focusing on the number and diversity of news story posts about substantive political issues. Using the newspapers’ print editions as a counterfactual, our results indicate an increase in the amount of substantive political news on Facebook by approximately 30%. This expansion occurred in a politically balanced way, except that the outlets disproportionately increased their Facebook coverage of the formerly underrepresented Linke (Left Party). Consequently, the within-outlet concentration of political viewpoints decreased by about one half of the standard deviation of our concentration indices.