  As civil discourse increasingly takes place online, misinformation and the
polarization of news shared in online communities have become ever more
relevant concerns with real world harms across our society. Studying online
news sharing at scale is challenging due to the massive volume of content which
is shared by millions of users across thousands of communities. Therefore,
existing research has largely focused on specific communities or specific
interventions, such as bans. However, understanding the prevalence and spread
of misinformation and polarization more broadly, across thousands of online
communities, is critical for the development of governance strategies,
interventions, and community design. Here, we conduct the largest study of news
sharing on reddit to date, analyzing more than 550 million links spanning 4
years. We use non-partisan news source ratings from Media Bias/Fact Check to
annotate links to news sources with their political bias and factualness. We
find that, compared to left-leaning communities, right-leaning communities have
105% more variance in the political bias of their news sources, and more links
to relatively-more biased sources, on average. We observe that reddit users'
voting and re-sharing behaviors generally decrease the visibility of extremely
biased and low factual content, which receives 20% fewer upvotes and 30% fewer
exposures from crossposts than more neutral or more factual content. This
suggests that reddit is more resilient to low factual content than Twitter. We
show that extremely biased and low factual content is very concentrated, with
99% of such content being shared in only 0.5% of communities, giving credence
to the recent strategy of community-wide bans and quarantines.
