Matthew A. Baum, David Lazer, Alexi Quintana, Roy Perlis, Katherine Ognyanova, James N. Druckman, John Della Volpe, and Mauricio Santillana. 7/20/2020. “How a Public Health Crisis Becomes a Public Trust Crisis.” Real Clear Politics. Publisher's Version
Irene Pasquetto, Matthew A. Baum, Eaman Jahani, and Alla Baranovsky. 5/27/2020. Understanding Misinformation on Mobile Instant Messengers (MIMs) in Developing Countries. Shorenstein Center. Cambridge: Harvard Kennedy School, Shorenstein Center of Media, Politics and Public Policy. Publisher's Version misinfo-on-mims-shorenstein-center-may-2020.pdf
Matthew A. Baum, Dara Kay Cohen, and Susanne Schwarz. 5/6/2020. “(Sex) Crime and Punishment: How Legally Irrelevant Details Influence Crime Reporting and Sanctioning Decisions.” Political Behavior. Publisher's Version
Recent prominent rape cases have raised concerns that the US exhibits a “culture of rape,” wherein victims are often disbelieved and blamed. We present an empirical conceptualization of rape culture, outlining four key features: blaming victims, empathizing with perpetrators, assuming the victims’ consent, and questioning victims’ credibility. In a series of experimental studies, we evaluate the relative impact of different types of rape culture biases on the reporting of rape, and how it is punished. We test how participants’ exposure to legally irrelevant details related to rape culture affects their decision-making. We find that exposure to certain details—relating to the victim’s consent and credibility—significantly decreasesparticipants’ propensities to recommend a rape case be reported to police or to advocate for a severe punishment for the perpetrator. The same biases do not emerge in robbery cases, suggesting that rape is regarded differently from other violent crimes.
Justin de Benedictis-Kessner, Matthew A. Baum, J. Berinsky, Adam, and Teppei Yamamoto. 11/2019. “Persuading the Enemy: Estimating the Persuasive Effects of Partisan Media with the Preference-Incorporating Choice and Assignment Design.” American Political Science Review, 113, 4, Pp. 902-916. Publisher's Version
Does media choice cause polarization, or merely reflect it? We investigate a critical aspect of this puzzle: how partisan media contribute to attitude polarization among different groups of media consumers. We implement a new experimental design, called the Preference-Incorporating Choice and Assignment (PICA) design, that incorporates both free choice and forced exposure. We estimate jointly the degree of polarization caused by selective exposure and the persuasive effect of partisan media. Our design also enables us to conduct sensitivity analyses accounting for discrepancies between stated preferences and actual choice, a potential source of bias ignored in previous studies using similar designs. We find that partisan media can polarize both its regular consumers and inadvertent audiences who would otherwise not consume it, but ideologically-opposing media potentially also can ameliorate existing polarization between consumers. Taken together, these results deepen our understanding of when and how media polarize individuals. 
Justin de Benedictis-Kessner, Matthew A. Baum, and Adam J. Berinsky. 5/9/2019. “Polarization and Media Usage: Disentangling Causality.” In Oxford Handbook of Electoral Persuasion. New York: Oxford University Press. Publisher's Version
This chapter examines the literature concerning media choice and partisan polarization.  The past few decades have seen enormous growth in the number of television and internet news sources, giving consumers dramatically increased choices.  Previous research has suggested two distinct links between media choice and partisan polarization: partisan media as a reflectionof polarization, as partisans self-select into media that conforms with their preexisting views, or as a causeof polarization, when outlets present one-sided stories that persuade people to adopt more extreme views.  This chapter discusses how the literature in these two research traditions has diverged, as well as more recent research attempting to bridge this divide.  Using novel methods, these studies have drawn together both self-selection and causal research designs to provide a more complete picture of media choice effects, and expanded the literature to more recent mediums, including the internet and social media.
Dean Knox, Teppei Yamamoto, Matthew A. Baum, and Adam Berinsky. 4/30/2019. “Design, Identification, and Sensitivity Analysis for Patient Preference Trials.” Journal of the American Statistical Association, 114, 528, Pp. 1532-1546. Publisher's Version

Social and medical scientists are often concerned that the external validity of experimental results may be compromised because of heterogeneous treatment effects. If a treatment has different effects on those who would choose to take it and those who would not, the average treatment effect estimated in a standard randomized controlled trial (RCT) may give a misleading picture of its impact outside of the study sample. Patient preference trials (PPTs), where participants’ preferences over treatment options are incorporated in the study design, provide a possible solution. In this paper, we provide a systematic analysis of PPTs based on the potential outcomes framework of causal inference. We propose a general design for PPTs with multi-valued treatments, where participants state their pre- ferred treatments and are then randomized into either a standard RCT or a self-selection condition. We derive nonparametric sharp bounds on the average causal effects among each choice-based sub- population of participants under the proposed design. We also propose a sensitivity analysis for the violation of the key ignorability assumption sufficient for identifying the target causal quantity. The proposed design and methodology are illustrated with an original study of partisan news media and its behavioral impact.

Matthew A. Baum and Yuri M. Zhukov. 4/9/2019. “Media Ownership and News Coverage of International Conflict.” Political Communication, 36, 1, Pp. 36-63. Publisher's Version
How do differences in ownership of media enterprises shape news coverage of international conflict? We examine this relationship using a new dataset of 591,532 articles on US-led multinational military operations in Libya, Iraq, Afghanistan and Kosovo, published by 2,505 newspapers in 116 countries. We find that ownership chains exert a homogenizing effect on the content of newspapers’ coverage of foreign policy, resulting in coverage across co-owned papers that is more similar in scope (what they cover), focus (how much “hard” relative to “soft” news they offer), and diversity (the breadth of topics they include in their coverage of a given issue) relative to coverage across papers that are not co-owned. However, we also find that competitive market pressures can mitigate these homogenizing effects, and incentivize co-owned outlets to differentiate their coverage. Restrictions on press freedom have the opposite impact, increasing the similarity of coverage within ownership chains.
Matthew A. Baum and Philip B. K. Potter. 4/2019. “Media, Public Opinion, and Foreign Policy in the Age of Trump.” Journal of Politics, 81, 2, Pp. 747-756. Publisher's Version

Democratic publics have always struggled to constrain their elected leaders’ foreign policy actions. By its nature, foreign policy creates information asymmetries that disadvantage citizens in favor of leaders. But has this disadvantage deepened with the advent of the Internet and the resulting fundamental changes in the media and politics? We argue that it has. The current information and political environments erode constraint by inclining constituents to reflexively and durably back “their” leaders and disapprove of opposition. These changes make it harder for citizens to informationally “catch up” with and constrain leaders because views that contradict citizens’ beliefs are less likely to break through when media are fragmented and siloed. These changes have important implications for theories concerning the democratic peace, audience costs, rally effects, and diversionary war. They may also contribute to instability in foreign policy by contributing to sudden and destabilizing changes in public opinion that undercut commitments abroad.

Matthew A. Baum and Dannagal G. Young. 2019. “The “Daily Them": Hybridity, Political Polarization and Presidential Leadership in a Digital Media Age.” In New Directions in Public Opinion Research, Third Edition. Routledge. Publisher's Version baumyoung_dailythem_proofs.pdf
Kenneth Joseph, Briony Swire-Thompson, Hannah Masuga, Matthew A. Baum, and David Lazer. 2019. “Polarized, Together: Comparing Partisan Support for Trump’s Tweets Using Survey and Platform-based Measures.” Thirteenth international AAAI conference on web and social media (ICWSM) 13 (1), Pp. 290-301. Munich, Germany: Association for the Advancement of Artificial Intelligence. Publisher's Version

Using both survey- and platform-based measures of support, we study how polarization manifests for 4,313 of President Donald Trump’s tweets since he was inaugurated in 2017. We find high levels of polarization in response to Trump’s tweets. However, after controlling for mean differences, we surprisingly find a high degree of agreement across partisan lines across both survey and platform-based measures. This suggests that Republicans and Democrats, while disagreeing on an absolute level, tend to agree on the relative quality of Trump’s tweets. We assess potential reasons for this, for example, by studying how support changes in response to tweets containing positive versus negative language.We also explore how Democrats and Republicans respond to tweets containing insults of individuals with particular socio-demographics, finding that Republican support decreases when Republicans, relative to Democrats, are insulted, and Democrats respond negatively to insults of women and members of the media.

Matthew A. Baum, Dara Kay Cohen, Susanne Schwarz, and Yuri Zhukov. 9/27/2018. “The way Kavanaugh’s supporters are talking about sexual assault allegations can be dangerous, our new study finds.” The Monkey Cage ( Publisher's Version the_way_kavanaughs_supporters_are_talking_about_sexual_assault_allegations_can_be_dangerous_our_ne.pdf
David M. J. Lazer, Matthew A. Baum, Yochai Benkler, Adam J. Berinsky, Kelly M. Greenhill, Filippo Menczer, Miriam J. Metzger, Brendan Nyhan, Gordon Pennycook, David Rothschild, Michael Schudson, Steven A. Sloman, Cass R. Sunstein, Emily A. Thorson, Duncan J. Watts, and Jonathan L. Zittrain. 3/2018. “The science of fake news.” Science, 359, 6380, Pp. 1094-1096. Publisher's Version
The rise of fake news highlights the erosion of long-standing institutional bulwarks against misinformation in the internet age. Concern over the problem is global. However, much remains unknown regarding the vulnerabilities of individuals, institutions, and society to manipulations by malicious actors. A new system of safeguards is needed. Below, we discuss extant social and computer science research regarding belief in fake news and the mechanisms by which it spreads. Fake news has a long history, but we focus on unanswered scientific questions raised by the proliferation of its most recent, politically oriented incarnation. Beyond selected references in the text, suggested further reading can be found in the supplementary materials.
science_of_fake_news.pdf science_supplemental_materials.pdf
Matthew Baum, Dara Kay Cohen, and Yuri M. Zhukov. 2018. “Does Rape Culture Predict Rape? Evidence from U.S. Newspapers, 2000-2013.” Quarterly Journal of Political Science, 13, 3, Pp. 263-289. Publisher's Version
We offer the first quantitative analysis of rape culture in the United States. Observers have long worried that biased news coverage of rape - which blames victims, empathizes with perpetrators, implies consent, and questions victims’ credibility - may deter victims from  coming forward, and ultimately increase the incidence of rape. We present a theory of how rape culture might shape the preferences and choices of perpetrators, victims and law enforcement, and test this theory with data on news stories about rape published in U.S. newspapers between 2000 and 2013. We find that rape culture in the media predicts both the  frequency of rape and its pursuit through the local criminal justice system. In jurisdictions where rape culture was more prevalent, there were more documented rape cases, but authorities were less vigilant in pursuing them. 
rapecultureqjps.doc rapecultureqjps_appendix.pdf
Matthew A. Baum and Yuri M. Zhukov. 2018. “Reporting Bias and Information Warfare”. Publisher's Version
International Studies Association Annual Convention
Matthew Baum, David Lazer, Nir Grinberg, Lisa Friedland, Kenneth Joseph, Will Hobbs, and Carolina Mattsson. 5/2017. “Combating Fake News: An Agenda for Research and Action.” In . Cambridge, MA: Shorenstein Center. Publisher's Version

Drawn from presentations by
Yochai Benkler (Harvard), Adam Berinsky (MIT), Helen Boaden (BBC), Katherine Brown (Council on Foreign Relations), Kelly Greenhill (Tufts and Harvard), David Lazer (Northeastern), Filippo Menczer (Indiana), Miriam Metzger (UC Santa Barbara), Brendan Nyhan (Dartmouth), Eli Pariser (UpWorthy), Gordon Pennycook (Yale), Lori Robertson (, David Rothschild (Microsoft Research), Michael Schudson (Columbia), Adam Sharp (formerly Twitter), Steven Sloman (Brown), Cass Sunstein (Harvard), Emily Thorson (Boston College), and Duncan Watts (Microsoft Research).

Executive Summary

Recent shifts in the media ecosystem raise new concerns about the vulnerability of democratic societies to fake news and the public’s limited ability to contain it. Fake news as a form of misinformation benefits from the fast pace that information travels in today’s media ecosystem, in particular across social media platforms. An abundance of information sources online leads individuals to rely heavily on heuristics and social cues in order to determine the credibility of information and to shape their beliefs, which are in turn extremely difficult to correct or change. The relatively small, but constantly changing, number of sources that produce misinformation on social media offers both a challenge for real-time detection algorithms and a promise for more targeted socio-technical interventions.

Matthew A. Baum. 2017. Report on Network Sunday Morning Talk Show Content and Ratings, Comparing 1983, 1999, and 2015. Publisher's Version
We studied the content and Nielsen ratings for interviews on the three network Sunday morning talk shows—Meet the Press (henceforth MTP), Face the Nation (FTN), and This Week (TW). We compared three time periods—1983 (MTP, FTN), 1999 (all three shows), and 2015 (all three shows). In order to insure apples-to-apples comparisons, for over time comparisons, we either restricted our analyses to MTP and FTN or analyzed the data with and without TW. For “overall” snapshots we included all three shows (MTP, FTN, TW). Our goals were fourfold: (1) identify any discernable trends in the topics and types of guests featured on the Sunday talk shows, (2) identify any trends in audience ratings, (3) assess whether and to what extent trends in topics and guests correlate with audience ratings, and (4) assess whether, to what extent, and under what circumstances, the Sunday talk shows influence the subsequent news agenda.
Matthew A Baum and Yuri M. Zhukov. 2015. “Filtering revolution: Reporting bias in international newspaper coverage of the Libyan civil war.” Journal of Peace Research . Publisher's Version
Reporting bias – the media’s tendency to systematically underreport or overreport certain types of events – is a persistent problem for participants and observers of armed conflict. We argue that the nature of reporting bias depends on how news organizations navigate the political context in which they are based. Where government pressure on the media is limited – in democratic regimes – the scope of reporting should reflect conventional media preferences toward novel, large-scale, dramatic developments that challenge the conventional wisdom and highlight the unsustainability of the status quo. Where political constraints on reporting are more onerous – in non-democratic regimes – the more conservative preferences of the state will drive the scope of coverage, emphasizing the legitimacy and inevitability of the prevailing order. We test these propositions using new data on protest and political violence during the 2011 Libyan uprising and daily newspaper coverage of the Arab Spring from 113 countries. We uncover evidence of a status-quo media bias in non-democratic states, and a revisionist bias in democratic states. Media coverage in non-democracies underreported protests and nonviolent collective action by regime opponents, largely ignored government atrocities, and overreported those caused by rebels. We find the opposite patterns in democratic states.
Matthew A. Baum and Philip B. K. Potter. 2015. War and Democratic Constraint: How the Public Influences Foreign Policy. Paperback, Pp. 280. Princeton University Press. Publisher's Version

Why do some democracies reflect their citizens' foreign policy preferences better than others? What roles do the media, political parties, and the electoral system play in a democracy's decision to join or avoid a war? War and Democratic Constraint shows that the key to how a government determines foreign policy rests on the transmission and availability of information. Citizens successfully hold their democratic governments accountable and a distinctive foreign policy emerges when two vital institutions—a diverse and independent political opposition and a robust media—are present to make timely information accessible.

Matthew Baum and Philip Potter demonstrate that there must first be a politically potent opposition that can blow the whistle when a leader missteps. This counteracts leaders' incentives to obscure and misrepresent. Second, healthy media institutions must be in place and widely accessible in order to relay information from whistle-blowers to the public. Baum and Potter explore this communication mechanism during three different phases of international conflicts: when states initiate wars, when they respond to challenges from other states, or when they join preexisting groups of actors engaged in conflicts.

Examining recent wars, including those in Afghanistan and Iraq, War and Democratic Constraint links domestic politics and mass media to international relations in a brand-new way.

baumpottercover.jpg war_and_democratic_constraint_chapter_1.pdf
Matthew A. Baum and Tim Groeling. 2013. “Partisan News Before Fox: Newspaper Partisanship and Partisan Polarization, 1881-1972 ”. Publisher's Version
How do partisan media affect polarization and partisanship? The rise of Fox News, MSNBC, and hyper-partisan outlets online gives this question fresh salience, but in this paper, we argue that the question is actually not new: prior to the broadcast era, newspapers dominated American mass communication. Many of these were identified as supporting one party over the other in their news coverage. While scholars have studied the composition and impact of the partisan press during their 19th-century height, the political impact of the gradual decline of these partisan papers remains relatively under-examined. The unnoted vitality and endurance of partisan newspapers (which constituted a majority of American newspapers until the 1960s) represents a huge hole in our understanding of how parties communicate. As a consequence of this omission, scholars have ignored a potentially vital contributing factor to changing patterns of partisan voting. In this paper, we examine both the degree and influence of partisanship in historical newspapers. We begin by content analyzing news coverage in the Los Angeles Times from 1885-1986 and the Atlanta Constitution from 1869-1945. To avoid problems of selection bias and the absence of a neutral baseline of coverage in the coded news, we focus on a subset of partisan news for which we have access to neutral coverage of a full population of potential stories: the obituaries of U.S. Senators. By coding whether and how the papers covered the deaths of these partisans over time, we are able to systematically test for bias. We then collect information on newspaper editorial stances from Editor and Publisher’s Annual Yearbook to examine the impact of newspaper partisanship on voting patterns in presidential elections from 1932-92. Specifically, we test whether the proportion of partisan news outlets in a given media market explains changes in the rate of polarized voting.
Matthew A. Baum and Philip B. K. Potter. 2013. “Looking for Audience Costs in all the Wrong Places: Electoral Institutions, Media Access, and Democratic Constraint.” The Journal of Politics . Publisher's Version
For leaders to generate credibility through audience costs, there must be mechanisms in place that enable citizens to learn about foreign policy failures. However, scholars have paid relatively little attention to variations among democracies in the extent to which the public is able to obtain this sort of information. We argue here that electoral institutions play this role by influencing the number of major political parties in a country and, with it, the extent and depth of opposition to the executive. Opposition leads to whistle-blowing, which makes it more likely that that the public will actually hear about a leader’s foreign policy blunders. The effectiveness of this whistle-blowing, however, is conditional on the public’s access to the primary conduit for communication between leaders and citizens: the mass media. We test these expectations statistically, demonstrating that leaders in systems with these attributes fare better with respect to their threats and the reciprocation of conflicts that they initiate. These findings suggest that democracies are not automatically able to generate credibility through audience costs and that the domestic institutions and political processes that link the public and leaders must be taken seriously.
potterbaumjopsupplementalappendix.pdf potterbaumjop.pdf