Social sciences: New users drove political polarization on the online social platform Reddit

New, largely right-wing users joining Reddit led to notable political polarization on the website around the 2016 US presidential election, according to an analysis of 5.1 billion comments posted over 14 years. These findings, published in Nature, challenge previous thinking that existing Reddit users drove polarization during this period.

Reddit is one of the world’s largest online social platforms, composed of thousands of discussion-based communities called subreddits. It has been suggested that being part of a like-minded group in an online community can lead to polarization, particularly involving political views. However, it is unclear whether individual users move towards ideological extremes over time, or populations with moderate views are replaced by users with more extreme views.

To investigate how polarization occurred on Reddit, Isaac Waller and Ashton Anderson developed a machine learning-based technique to assess the social stances, including political leanings, of all Reddit posts made between 2005 and 2018 across about 10,000 different subreddit communities. The authors found that, although the views of individual users generally did not polarize over time, the platform saw synchronized political polarization around the time of the 2016 US Presidential election. This mass polarization was disproportionately driven by new and newly political users on the right of the political spectrum. These new users shifted right-wing discussions further to the right, whereas left-wing and centre discussions were not affected.

This approach to quantifying social stances in online communities could have implications for understanding the social contexts of online behaviour and the design of online platforms, according to the authors. The findings suggest that sometimes observations, such as increased polarization, may be due to changing dynamics of the specific population rather than a society-level change in beliefs.