SignificanceSocial media sites are often blamed for exacerbating political polarization by creating “echo chambers” that prevent people from being exposed to information that contradicts their preexisting beliefs. We conducted a field experiment that offered a large group of Democrats and Republicans financial compensation to follow bots that retweeted messages by elected officials and opinion leaders with opposing political views. Republican participants expressed substantially more conservative views after following a liberal Twitter bot, whereas Democrats’ attitudes became slightly more liberal after following a conservative Twitter bot—although this effect was not statistically significant. Despite several limitations, this study has important implications for the emerging field of computational social science and ongoing efforts to reduce political polarization online.

Do advocacy organizations stimulate public conversation about social problems by engaging in rational debate, or by appealing to emotions? We argue that rational and emotional styles of communication ebb and flow within public discussions about social problems due to the alternating influence of social contagion and saturation effects. These "cognitive-emotional currents" create an opportunity structure whereby advocacy organizations stimulate more conversation if they produce emotional messages after prolonged rational debate or vice versa. We test this hypothesis using automated text-analysis techniques that measure the frequency of cognitive and emotional language within two advocacy fields on Facebook over 1.5 years, and a web-based application that offered these organizations a complimentary audit of their social media outreach in return for sharing nonpublic data about themselves, their social media audiences, and the broader social context in which they interact. Time-series models reveal strong support for our hypothesis, controlling for 33 confounding factors measured by our Facebook application. We conclude by discussing the implications of our findings for future research on public deliberation, how social contagions relate to each other, and the emerging field of computational social science.

Among the many remarkable political developments in the United States of the past few years, one will surely stand out to future scholars of race, law, and cities: the significant mobilization against police violence associated with the Black Lives Matter movement. Gaining ground in the aftermath of protests and civil disturbances prompted by the police killing of Michael Brown in Ferguson, Missouri, in August of 2014 and the failure of a Staten Island grand jury later that year to indict the officers involved in the death of Eric Garner, by 2015 the Black Lives Matter movement had become a force to be reckoned with. In the Democratic presidential primaries, all the candidates staked out policy positions on racial inequalities in policing and criminal justice. In cities around the country, mayors and police chiefs were forced to address accusations of police bias, often following incidents caught on video and spread widely through social media. Public opinion shifted as well. A Gallup poll released in June 2015 showed that public confidence in the police had plummeted to record low levels not seen since the trials of the officers who took part in the arrest and beating of Rodney King in 1991 (Jones 2015). As the Black Lives Matter movement picked up, however, another thread emerged in the public conversation. The year 2015 also saw a non-negligible increase in violent crime in some U.S. cities. Although at the national level crime remained low, with analysts pointing out that after 20 years of declines a floor in crime rates may have been reached around which one would naturally expect some fluctuation, other commentators and public officials expressed alarm. Some linked the uptick to the protest movement against police violence, coining the term Ferguson effect to refer to a hypothesized chain of events where (in the most popular version of the argument) public anger at police mistreatment of African Americans would lead police officers to be more circumspect in their behaviors in high-crime neighborhoods with large black populations. As police pulled back from discretionary activity such as "stop and frisk" or investigatory traffic stops, criminals would find expanded opportunities. The Ferguson effect hypothesis also proved politically powerful. FBI Director James Comey said he believed it to be true. After the targeted killings of five police officers in 703122S RDXXX10.

The decline in trust in the scientific community in the United States among political conservatives has been well established. But this observation is complicated by remarkably positive and stable attitudes toward scientific research itself. What explains the persistence of positive belief in science in the midst of such dramatic change? By leveraging research on the performativity of conservative identity, we argue that conservative scientific institutions have manufactured a scientific cultural repertoire that enables participation in this highly valued epistemological space while undermining scientific authority perceived as politically biased. We test our hypothesized link between conservative identity and scientific perceptions using panel data from the General Social Survey. We find that those with stable conservative identities hold more positive attitudes toward scientific research while simultaneously holding more negative attitudes towards the scientific community compared to those who switch to and from conservative political identities. These findings support a theory of a conservative scientific repertoire that is learned over time and that helps orient political conservatives in scientific debates that have political repercussions. Implications of these findings are discussed for researchers interested in the cultural differentiation of scientific authority and for stakeholders in scientific communication and its public policy.

There is mounting concern that social media sites contribute to political polarization by creating "echo chambers" that insulate people from opposing views about current events. We surveyed a large sample of Democrats and Republicans who visit Twitter at least three times each week about a range of social policy issues. One week later, we randomly assigned respondents to a treatment condition in which they were offered financial incentives to follow a 1 Twitter bot for one month that exposed them to messages produced by elected officials, organizations, and other opinion leaders with opposing political ideologies. Respondents were re-surveyed at the end of the month to measure the effect of this treatment, and at regular intervals throughout the study period to monitor treatment compliance. We find that Republicans who followed a liberal Twitter bot became substantially more conservative post-treatment, and Democrats who followed a conservative Twitter bot became slightly more liberal post-treatment. These findings have important implications for the interdisciplinary literature on political polarization as well as the emerging field of computational social science.Political polarization in the United States has become a central focus of social scientists in recent decades (1-7). Americans remain deeply divided on controversial issues such as inequality, race, and immigration. According to the 2016 National Election Study, 59.3% of Clinton voters believe federal aid to the poor should be increased compared to only 20.2% of Trump voters. 77.7% of Clinton voters express favorable attitudes towards the Black Lives Matter movement, whereas 31.2% of Trump voters do the same. 68.9% of Trump voters believe immigration to the United States should be decreased, compared to 21.9% of Clinton voters.Longstanding divides about these and many other issues have far-reaching consequences for the design and implementation of social policies as well as the effective function of democracy more broadly (8-12).America's deep partisan divides are often attributed to "echo chambers," or patterns of information sharing that reinforce pre-existing political beliefs by limiting exposure to heterogeneous ideas and perspectives (13)(14)(15)(16)(17). Concern about selective exposure to information and political polarization has increased in the age of social media (13,(18)(19)(20). The vast majority of Americans now visit a social media site at least once each day, and a rapidly growing number 2 of them list social media as their primary source of news (21). Despite initial optimism that social media might enable people to consume more heterogeneous sources of information about current events, there is growing concern that such forums exacerbate political polarization because of social network homophily, or the well-documented tendency of people to form social network ties to those who are similar to themselves (22, 23). The endogenous relationship between social network formation and political attitudes also creates formidable challenges f...