Pablo Barberá

Computational Political Scientist



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I am a Research Scientist in Facebook's Core Data Science team and an Associate Professor in the Department of Political Science and International Relations at the University of Southern California. I am also a Visiting Fellow in the Methodology department at the London School of Economics. I received my PhD in Political Science from New York University in 2015, where I was also a graduate research associate in the Social Media and Political Participation lab and a Moore-Sloan Post-Doctoral Fellow at the NYU Center for Data Science. My primary areas of academic research include social media and politics, computational social science, and comparative electoral behavior and political representation.

Selected publications

Who Leads? Who Follows? Measuring Issue Attention and Agenda Setting by Legislators and the Mass Public Using Social Media Data.

American Political Science Review, 2019.
Co-authored with Andreu Casas, Jonathan Nagler, Patrick J. Egan, Richard Bonneau, John T. Jost, and Joshua Tucker

Link | Supplementary Materials | Topic visualization demo | Replication code and data | Expand abstract »

Are legislators responsive to the priorities of the public? Research demonstrates a strong correspondence between the issues about which the public cares and the issues addressed by politicians, but conclusive evidence about who leads whom in setting the political agenda has yet to be uncovered. We answer this question with fine-grained temporal analyses of Twitter messages by legislators and the public during the 113th US Congress. After employing an unsupervised method that classifies tweets sent by legislators and citizens into topics, we use vector autoregression models to explore whose priorities more strongly predict the relationship between citizens and politicians. We find that legislators are more likely to follow, than to lead, discussion of public issues, results that hold even after controlling for the agenda-setting effects of the media. We also find, however, that legislators are more likely to be responsive to their supporters than to the general public.

Explaining the Spread of Misinformation on Social Media: Evidence from the 2016 U.S. Presidential Election

APSA Comparative Politics Newsletter, 2018.

Link | Complete newsletter | Expand abstract »

This short note examines the empirical evidence regarding the prevalence of misinformation on Twitter in the United States during the 2016 elections. Data from Twitter accounts matched with voter records show that old people and registered Republicans are significantly more likely to share links to false news stories than other groups.

The Consequences of Exposure to Disinformation and Propaganda in Online Settings

Chapter in joint report sponsored by the Hewlett Foundation and edited by Joshua Tucker, 2018.

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The Hewlett Foundation commissioned this report to provide an overview of the current state of the literature on the relationship between social media; political polarization; and political "disinformation," a term used to encompass a wide range of types of information about politics found online, including "fake news," rumors, deliberately factually incorrect information, inadvertently factually incorrect information, politically slanted information, and "hyperpartisan" news. The full list of authors is: Joshua A. Tucker, Andrew Guess, Pablo Barberá, Cristian Vaccari, Alexandra Siegel, Sergey Sanovich, Denis Stukal, and Brendan Nyhan

From Liberation to Turmoil: Social Media and Democracy

Journal of Democracy, 2017.
Co-authored with Joshua Tucker, Yannis Theocharis, and Margaret Roberts.

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How can one technology—social media—simultaneously give rise to hopes for liberation in authoritarian regimes, be used for repression by these same regimes, and be harnessed by antisystem actors in democracy? We present a simple framework for reconciling these contradictory developments based on two propositions: 1) that social media give voice to those previously excluded from political discussion by traditional media, and 2) that although social media democratize access to information, the platforms themselves are neither inherently democratic nor nondemocratic, but represent a tool political actors can use for a variety of goals, including, paradoxically, illiberal goals.

The New Public Address System: Why Do World Leaders Adopt Social Media?

International Studies Quarterly, 2017.
Co-authored with Thomas Zeitzoff.

Link | Preprint | Online Appendix | Replication materials | Expand abstract »

The emergence of social media - and in particular Twitter and Facebook - has led scholars to focus on its effects on mass behavior and protest. Yet an important, and unanswered question is what explains the variation in the adoption and use of social media by world leaders? By the end of 2014, over 76% of world leaders had an active presence on social media, and used their accounts to communicate with domestic and international audiences. We look at several different potential hypotheses that explain adoption of social media by world leaders including: modernization, social pressure, level of democratization, and diffusion. We find strong support that increased political pressure from social unrest and higher levels of democratization are both associated with leader adoption of social media platforms. Although the association we identify is not causal, these findings reveal the relationship between institutional and political pressures and the political communication of country leaders.

The Critical Periphery in the Growth of Social Protests

PLOS ONE, 2015, 10 (11).
Co-authored with Ning Wang, Richard Bonneau, John T. Jost, Jonathan Nagler, Joshua Tucker and Sandra González-Bailón

Link | Online appendix | Replication data | Expand abstract »

Social media have provided instrumental means of communication in many recent political protests. The efficiency of online networks in disseminating timely information has been praised by many commentators; at the same time, users are often derided as “slacktivists” because of the shallow commitment involved in clicking a forwarding button. Here we consider the role of these peripheral online participants, the immense majority of users who surround the small epicenter of protests, representing layers of diminishing online activity around the committed minority. We analyze three datasets tracking protest communication in different languages and political contexts through the social media platform Twitter and employ a network decomposition technique to examine their hierarchical structure. We provide consistent evidence that peripheral participants are critical in increasing the reach of protest messages and generating online content at levels that are comparable to core participants. Although committed minorities may constitute the heart of protest movements, our results suggest that their success in maximizing the number of online citizens exposed to protest messages depends, at least in part, on activating the critical periphery. Peripheral users are less active on a per capita basis, but their power lies in their numbers: their aggregate contribution to the spread of protest messages is comparable in magnitude to that of core participants. An analysis of two other datasets unrelated to mass protests strengthens our interpretation that core-periphery dynamics are characteristically important in the context of collective action events. Theoretical models of diffusion in social networks would benefit from increased attention to the role of peripheral nodes in the propagation of information and behavior.

Tweeting from Left to Right: Is Online Political Communication More Than an Echo Chamber?

Psychological Science, 2015, 26 (10), 1531-1542.
Co-authored with John T. Jost, Jonathan Nagler, Joshua Tucker, and Richard Bonneau.

Link | Online appendix | Replication materials and data | Expand abstract »

We estimated ideological preferences of 3.8 million Twitter users and, using a dataset of 150 million tweets concerning 12 political and non-political issues, explored whether online communication resembles an "echo chamber" due to selective exposure and ideological segregation or a "national conversation." We observed that information was exchanged primarily among individuals with similar ideological preferences for political issues (e.g., presidential election, government shutdown) but not for many other current events (e.g., Boston marathon bombing, Super Bowl). Discussion of the Newtown shootings in 2012 reflected a dynamic process, beginning as a "national conversation" before being transformed into a polarized exchange. With respect to political and non-political issues, liberals were more likely than conservatives to engage in cross-ideological dissemination, highlighting an important asymmetry with respect to the structure of communication that is consistent with psychological theory and research. We conclude that previous work may have overestimated the degree of ideological segregation in social media usage.

Birds of the Same Feather Tweet Together. Bayesian Ideal Point Estimation Using Twitter Data.

Political Analysis, 2015, 23 (1), 76-91

Link | Pre-print | Online appendix | Replication materials | GitHub tutorial | Expand abstract »

Politicians and citizens increasingly engage in political conversations on social media outlets such as Twitter. In this paper I show that the structure of the social networks in which they are embedded can be a source of information about their ideological positions. Under the assumption that social networks are homophilic, I develop a Bayesian Spatial Following model that considers ideology as a latent variable, whose value can be inferred by examining which politics actors each user is following. This method allows us to estimate ideology for more actors than any existing alternative, at any point in time and across many polities. I apply this method to estimate ideal points for a large sample of both elite and mass public Twitter users in the US and five European countries. Thee estimated positions of legislators and political parties replicate conventional measures of ideology. The method is also able to successfully classify individuals who state their political preferences publicly and a sample of users matched with their party registration records. To illustrate the potential contribution of these estimates, I examine the extent to which online behavior during the 2012 US presidential election campaign is clustered along ideological lines.