  A growing number of people engage in online health forums, making it
important to understand the quality of the advice they receive. In this paper,
we explore the role of expertise in responses provided to help-seeking posts
regarding mental health. We study the differences between (1) interactions with
peers; and (2) interactions with self-identified mental health professionals.
First, we show that a classifier can distinguish between these two groups,
indicating that their language use does in fact differ. To understand this
difference, we perform several analyses addressing engagement aspects,
including whether their comments engage the support-seeker further as well as
linguistic aspects, such as dominant language and linguistic style matching.
Our work contributes toward the developing efforts of understanding how health
experts engage with health information- and support-seekers in social networks.
More broadly, it is a step toward a deeper understanding of the styles of
interactions that cultivate supportive engagement in online communities.
