  Virtual humans need to be persuasive in order to promote behaviour change in
human users. While several studies have focused on understanding the numerous
aspects that influence the degree of persuasion, most of them are limited to
dyadic interactions. In this paper, we present an evaluation study focused on
understanding the effects of multiple agents on user's persuasion. Along with
gender and status (authoritative & peer), we also look at type of focus
employed by the agent i.e., user-directed where the agent aims to persuade by
addressing the user directly and vicarious where the agent aims to persuade the
user, who is an observer, indirectly by engaging another agent in the
discussion. Participants were randomly assigned to one of the 12 conditions and
presented with a persuasive message by one or several virtual agents. A
questionnaire was used to measure perceived interpersonal attitude, credibility
and persuasion. Results indicate that credibility positively affects
persuasion. In general, multiple agent setting, irrespective of the focus, was
more persuasive than single agent setting. Although, participants favored
user-directed setting and reported it to be persuasive and had an increased
level of trust in the agents, the actual change in persuasion score reflects
that vicarious setting was the most effective in inducing behaviour change. In
addition to this, the study also revealed that authoritative agents were the
most persuasive.
