Abstract: There is widespread concern that the online news ecosystem produces highly polarized content and that extreme content gets further amplified through social media distribution channels. Methodological limitations in estimating content-based slant at the article level have made evaluating these claims difficult. We use data on the near universe (circa 1 million) of hard news articles published online by the top 100 U.S. news outlets in 2019, together with recent advances in natural language processing, to obtain a content-based measure of slant at the article level. Our main finding is that the degree of polarization in news consumption on social media is arguably high. Specifically, the mean slant difference between articles consumed by conservative and liberal users is 1.5 times the ideological distance between the average New York Times and Foxnews.com article. We also show that: i) the majority (65%) of the variance in slant across articles arises within outlets, rather than across outlets, thus highlighting the importance of measuring slant at the article rather than the outlet level. ii) Most news produced is centrist, but the tails of the slant distribution are thick and there is substantial variation in slant across news type and topic. iii) Extreme content is much more likely to be shared widely on Facebook than moderate content. iv) There is substantial pro-attitudinal news exposure and consumption on Facebook even within the same outlet. v) The articles that liberals and conservatives are exposed to on their Facebook feeds are already highly polarized. vi) Echo chambers play an important role in driving polarized news consumption on Facebook.

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