How Social Media Reduces Mass Political Polarization . Evidence from Germany , Spain , and the U

A growing proportion of citizens rely on social media to gather political information and to engage in political discussions within their personal networks. Existing studies argue that social media create “echo-chambers,” where individuals are primarily exposed to likeminded views. However, this literature has ignored that social media platforms facilitate exposure to messages from those with whom individuals have weak ties, which are more likely to provide novel information to which individuals would not be exposed otherwise through offline interactions. Because weak ties tend to be with people who are more politically heterogeneous than citizens’ immediate personal networks, this exposure reduces political extremism. To test this hypothesis, I develop a new method to estimate dynamic ideal points for social media users. I apply this method to measure the ideological positions of millions of individuals in Germany, Spain, and the United States over time, as well as the ideological composition of their personal networks. Results from this panel design show that most social media users are embedded in ideologically diverse networks, and that exposure to political diversity has a positive effect on political moderation. This result is robust to the inclusion of covariates measuring offline political behavior, obtained by matching Twitter user profiles with publicly available voter files in several U.S. states. I also provide evidence from survey data in these three countries that bolsters these findings. Contrary to conventional wisdom, my analysis provides evidence that social media usage reduces mass political polarization. ∗Pablo Barberá (www.pablobarbera.com) is a Moore-Sloan Fellow at the NYU Center for Data Science. Mass political polarization is a signature phenomenon of our time. As such, it has received considerable scholarly and journalistic attention in recent years (see e.g. Abramowitz and Saunders, 2008 and Fiorina and Abrams, 2008). A growing body of work argues that the introduction of the Internet as a relevant communication tool is contributing to this trend (Farrell, 2012). Empirical evidence of persistent ideological sorting in online communication networks (Adamic and Glance, 2005; Conover et al., 2012; Colleoni, Rozza and Arvidsson, 2014) has been taken to suggest that Internet use may exacerbate mass political polarization. As Sunstein (2001) or Hindman (2008) argue, the Internet appears to create communities of like-minded individuals where cross-ideological interactions and exposure to political diversity are rare. This argument builds upon a long tradition of research that shows that political discussion in homogenous communication networks reinforces individuals’ existing attitudes (Berelson, Lazarsfeld and McPhee, 1954; Huckfeldt, 1995; Mutz, 2006) In this paper I challenge this conventional wisdom. I contend that social media usage – one of the most frequent online activities – reduces political polarization, and I provide empirical evidence to support this claim. My argument is two-fold. First, social media platforms like Facebook or Twitter increase incidental exposure to political messages shared by peers. Second, these sites facilitate exposure to messages from those with whom individuals have weak social ties (Granovetter, 1973), which are more likely to provide novel information. Consequently, despite the homophilic nature of personal networks (McPherson, Smith-Lovin and Cook, 2001), social media leads to exposure to a wider range of political opinions than one would normally encounter offline. This induces political moderation at the individual level and, counter intuitively, helps to decrease mass political polarization. To test this hypothesis, I develop a new method to measure the ideological positions of Twitter users at any point in time, and apply it to estimate the ideal points of millions of citizens in three countries with different levels of mass political polarization (Germany, Spain, and the United States). This measure allows me to observe not only how their political preferences evolve, but also the ideological composition of their communication networks. My approach represents a crucial improvement over survey studies of political networks, which often ask only about close discussion partners and in practice exclude weak ties, limiting researchers’ ability to study their influence. In addition, I rely on name identification techniques to match Twitter users with publicly available voter files in the states of Arkansas, California, Florida, Ohio, and Pennsylvania. This allows me to demonstrate that my results are not confounded by covariates measuring