Social media allow experts to form communities and engage in direct dialogue with publics, which can promote mutual understanding between sciences and publics. However, little is known about experts' participation in online communities, or effective ways to prepare them for public engagement. Here, we explored these issues with experts who voluntarily engage with publics on social media, to understand their public engagement practices. Stimulated recall interviews were conducted with 20 experts who participate in question-and-answer Facebook groups dedicated to vaccines and nutrition. The findings suggest that experts employ diverse considerations in their outreach, partly to establish epistemic trustworthiness. These can be grouped into three goals and two constraints: countering misinformation, establishing benevolence, and establishing competence while maintaining integrity and clarity. Empathic failure and burnout both emerged as factors that impair establishing benevolence. We discuss implications for community-level science literacy and for preparing scientists for "bounded engagement with publics."
Keywords: nutrition; online communities; outreach; science literacy; social media; trustworthiness; vaccines.