  This paper investigates the effects of seeing ideas presented in-person when
they are easily accessible online. Presentations may increase the diffusion of
ideas intentionally (when one attends the presentation of an idea of interest)
and serendipitously (when one sees other ideas presented in the same session).
We measure these effects in the context of 25 computer science conferences
using data from the scheduling application Confer, which lets users browse
papers, Like those of interest, and receive schedules of their presentations.
We address endogeneity concerns in presentation attendance by exploiting
scheduling conflicts: when a user Likes multiple papers that are presented at
the same time, she cannot see them both, potentially affecting their diffusion.
Estimates show that being able to see presentations increases citing of Liked
papers within two years by 1.5 percentage points (62.5% boost over the baseline
citation rate). Attention to Liked papers also spills over to non-Liked papers
in the same session, increasing their citing by 0.5 percentage points (125%
boost), and this serendipitous diffusion represents 30.5% of the total effect.
Both diffusion types were concentrated among papers semantically close to an
attendee's prior work, suggesting that there are inefficiencies in finding
related research that conferences help overcome. Overall, even when ideas are
easily accessible online, in-person presentations substantially increase
diffusion, much of it serendipitous.
