  This paper examines the link between conversational communities on Twitter
and their members' expressions of social identity. It specifically tests the
presence of community prototypes, or collections of attributes which define a
group through meta-contrast: high in-group cohesiveness and high out-group
distinctiveness. Analyzing four datasets of political discussions ranging from
roughly 4 to 30 million tweets, we find strong evidence for the presence of
distinctive community prototypes. We observe that community prototypes are
constructed through hashtags, mentions, emojis, and identity-phrases. This
finding situates prior work on the identity signaling of individual users
within a larger group process playing out within communication communities.
Community prototypes are then constructed for specific communities by measuring
the salience of identity signals for each community. Observed community
prototypes tend to be based on political ideology, location and language, or
general interests. While the presence of community prototypes may be a natural
group behavior, the high levels of contrast observed between communities
displaying ideologically opposed prototypes indicate the presence of
identity-related polarization.
