Working Paper
Matthew A. Baum, Bryce Jensen Dietrich, Rebecca Goldstein, and Maya Sen. Working Paper. “Estimating the Effect of Asking About Citizenship on the U.S. Census: Results from a Randomized Controlled Trial”. Publisher's Version

The 2020 U.S. Census will, for the first time since 1950, ask about residents’ citizenship status.The effect of doing so on census completion across different racial/ethnic groups is, however, unknown. Leveraging a survey experiment (n = 9,035 respondents) we are the first to assess the causal effect of this question change. We find that asking about citizenship status significantly increases the percent of questions skipped, with particularly strong effects among Hispanics, and makes respondents less likely to report having members of their household who are of Hispanic ethnicity. Although our study is not designed to address household size effects, when we extrapolate to the general population, our results imply that asking about citizenship will reduce the number of Hispanics reported in the 2010 Census by approximately 4.2 million, or around 8.4 percent of the 2010 Hispanic population.

David Lazer, Jonathan Green, Matthew A. Baum, Alexi Quintana Mathé, Katherine Ognyanova, Adina Gitomer, James N. Druckman, Matthew Simonson, Hanyu Chwe, Roy H. Perlis, Jennifer Lin, and Mauricio Santillana. 10/21/2020. “These nine swing states will see the biggest ‘blue shift’ as ballots are counted after the election.” The Washington Post Monkey Cage. Publisher's Version
Matthew A. Baum. 6/28/2020. “Trump Still Has Approval Ratings Far Higher than George Bush. Here's Why.” Los Angeles Times. Publisher's Version
See also: Op-Eds, Politics
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.
Matthew A. Baum, Katherine Ognyanova, and David Lazer. 4/29/2020. “These Three Governors are Reopening Their States Faster than Their Voters Want: That's What Our Polling Found in Florida, Georgia, and Tennessee.” The Washington Post Monkey Cage. Publisher's Version
Matthew A. Baum. 3/30/2020. “Trump's Coronavirus Approval Rating: Why its Going Up.” Los Angeles Times. Publisher's Version
See also: Op-Eds, Politics
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. 
Matthew A. Baum, Dannagal G. Young, and Duncan Prettyman. 5/13/2019. “vMOBilize: Gamifying Civic Learning and Political Engagement in a Classroom Context.” Journal of Political Science Education. Publisher's Version

This study presents the results of a quasi-experiment (N= 307) conducted over the course of 10 weeks in Spring of 2016 to assess the effectiveness of a game platform designed to facilitate political engagement, attention, efficacy, knowledge, and participation among college students. Results indicate positive effects of gameplay on several key dimensions of political engagement, including voter registration, virtual political participation (following a candidate on Twitter, liking a candidate on Facebook, and watching debates), and consumption of public affairs information (including National Public Radio, non-NPR political talk radio, and online news aggregator sites). Additionally, gameplay provided significantly greater benefits to students with the lowest rates of political knowledge at baseline. Overall, participants reported high rates of game satisfaction, with 79% of participants reporting being very to somewhat pleased if they were asked to play the game again. These results are discussed in terms of the implications for civics education, pedagogy, and political engagement among young people.

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.
Matthew Barreto, Chris Warshaw, Matthew A. Baum, Bryce J. Dietrich, Rebecca Goldstein, and Maya Sen. 4/22/2019. “New Research Shows Just How Badly a Citizenship Question Would Hurt the 2020 Census.” Washington Post Monkey Cage. Publisher's Version
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 (Washingtonpost.com). Publisher's Version the_way_kavanaughs_supporters_are_talking_about_sexual_assault_allegations_can_be_dangerous_our_ne.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 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 (FactCheck.org), 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 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
Matthew A. Baum. 2012. “Partisan Media and Attitude Polarization: The Case of Healthcare Reform.” In Regulatory Breakdown The Crisis of Confidence in U.S. Regulation. University of Pennsylvania Press. Publisher's Version