Methods
RECRUITMENT, APPENDIX
We hired the survey firm YouGov to recruit self-identified Democrats who were told they had been randomly selected for an opportunity to earn $10 for testing a new app. Recruitment started on February 28, 2020, and the app, called UniteDem, was described as a way for Democrats to anonymously discuss which candidate was best positioned to defeat Donald Trump in the general election. Respondents were asked to install UniteDem on an iOS or Android mobile device and given an invite code that we used to assign them to one of several treatment conditions described below. Figure 
Screenshots of the Social Media Platform Used in Study. 596 Democrats were recruited to download an app. They completed a survey about their views about presidential candidates and were instructed to discuss which one was best positioned to defeat Trump in the 2020 Democratic Primary election. After completing the in-app survey, some respondents were randomly assigned an avatar (seen only by their discussion partner) that was inconsistent with their self-reported gender. After a 14 exchange chat with another Democrat in the study, respondents completed a post-survey of their attitudes.Next, respondents were redirected to a screen that presented a brief video in which a series of male and female silhouettes circled around while informing the user that the app was searching for a discussion partner (see Fig. Conversations ended after the participants had completed 14 exchanges, where an “exchange” is defined as one user sending one message or a few successive messages followed by one or more successive messages from the other user, or at 7 pm eastern standard time on March 3, 2020 (Super Tuesday) if they had not yet completed all exchanges. All conversations where both participants completed the post survey before the Super Tuesday deadline are included in the analysis; our results are robust to excluding the eleven conversations with fewer than 14 exchanges, see Supplemental Appendix Sect. Following the conversation, the app asked respondents (N = 596; attrition is addressed in the All of our research was approved by the Institutional Review Board at Duke University. Respondents provided informed consent to participate and were debriefed about the nature of the study and experimental manipulation after the conclusion of the experiment. All methods were performed in accordance with the relevant guidelines and regulations.