Title: Political Discourse on Social Media: Echo Chambers, Gatekeepers, and the Price of Bipartisanship,
Abstract: Echo chambers, i.e., situations where one is exposed only to opinions that
agree with their own, are an increasing concern for the political discourse in
many democratic countries. This paper studies the phenomenon of political echo
chambers on social media. We identify the two components in the phenomenon: the
opinion that is shared ('echo'), and the place that allows its exposure
('chamber' --- the social network), and examine closely at how these two
components interact. We define a production and consumption measure for
social-media users, which captures the political leaning of the content shared
and received by them. By comparing the two, we find that Twitter users are, to
a large degree, exposed to political opinions that agree with their own. We
also find that users who try to bridge the echo chambers, by sharing content
with diverse leaning, have to pay a 'price of bipartisanship' in terms of their
network centrality and content appreciation. In addition, we study the role of
'gatekeepers', users who consume content with diverse leaning but produce
partisan content (with a single-sided leaning), in the formation of echo
chambers. Finally, we apply these findings to the task of predicting partisans
and gatekeepers from social and content features. While partisan users turn out
relatively easy to identify, gatekeepers prove to be more challenging.