“Does Online Partisan Media Affect Attitudes and Behavior?” Abstract: In today’s fragmented online media ecosystem, does exposure to political news through partisan media have a measurable effect on citizens’ political attitudes and behavior? Or are these outlets merely preaching to the choir? And if such media effects exist, are they durable and homogeneous across political groups? To answer these questions, we conducted a pre-registered, randomized field experiment  embedded in a nationally representative online panel survey. We incentivized participants to temporarily alter features of their information environment during the 2018 U.S. midterm election campaign. Subjects in the treatment groups were asked to change their default browser homepage to either FoxNews.com or HuffPost.com. Using web browsing data collected for our respondents, we find that our intervention exogenously and durably altered news consumption habits. We then evaluate how our treatment affected political attitudes, voting behavior, and civic knowledge, which we measure based on survey responses collected at periodic intervals after our intervention, up to one year later. Our results generally show negligible persuasive and agenda-setting effects, consistent with the minimal media effects hypothesis. However, we uncover a meaningful decrease in overall media trust among those exposed to Fox News and an increase in support for liberal immigration policies among those in the Huffington Post treatment group. Find out more about Prof. Barberá