  Social media have great potential to support diverse information sharing, but
there is widespread concern that platforms like Twitter do not result in
communication between those who hold contradictory viewpoints. Because users
can choose whom to follow, prior research suggests that social media users
exist in 'echo chambers' or become polarized. We seek evidence of this in a
complete cross section of hyperlinks posted on Twitter, using previously
validated measures of the political slant of news sources to study information
diversity. Contrary to prediction, we find that the average account posts links
to more politically moderate news sources than the ones they receive in their
own feed. However, members of a tiny network core do exhibit cross-sectional
evidence of polarization and are responsible for the majority of tweets
received overall due to their popularity and activity, which could explain the
widespread perception of polarization on social media.
