  A growing body of work has highlighted the important role that Wikipedia's
volunteer-created content plays in helping search engines achieve their core
goal of addressing the information needs of millions of people. In this paper,
we report the results of an investigation into the incidence of Wikipedia links
in search engine results pages (SERPs). Our results extend prior work by
considering three U.S. search engines, simulating both mobile and desktop
devices, and using a spatial analysis approach designed to study modern SERPs
that are no longer just "ten blue links". We find that Wikipedia links are
extremely common in important search contexts, appearing in 67-84% of all SERPs
for common and trending queries, but less often for medical queries.
Furthermore, we observe that Wikipedia links often appear in "Knowledge Panel"
SERP elements and are in positions visible to users without scrolling, although
Wikipedia appears less in prominent positions on mobile devices. Our findings
reinforce the complementary notions that (1) Wikipedia content and research has
major impact outside of the Wikipedia domain and (2) powerful technologies like
search engines are highly reliant on free content created by volunteers.
