  Wikipedia, the free online encyclopedia that anyone can edit, is one of the
most visited sites on the Web and a common source of information for many
users. As an encyclopedia, Wikipedia is not a source of original information,
but was conceived as a gateway to secondary sources: according to Wikipedia's
guidelines, facts must be backed up by reliable sources that reflect the full
spectrum of views on the topic. Although citations lie at the very heart of
Wikipedia, little is known about how users interact with them. To close this
gap, we built client-side instrumentation for logging all interactions with
links leading from English Wikipedia articles to cited references during one
month, and conducted the first analysis of readers' interaction with citations
on Wikipedia. We find that overall engagement with citations is low: about one
in 300 page views results in a reference click (0.29% overall; 0.56% on
desktop; 0.13% on mobile). Matched observational studies of the factors
associated with reference clicking reveal that clicks occur more frequently on
shorter pages and on pages of lower quality, suggesting that references are
consulted more commonly when Wikipedia itself does not contain the information
sought by the user. Moreover, we observe that recent content, open access
sources and references about life events (births, deaths, marriages, etc) are
particularly popular. Taken together, our findings open the door to a deeper
understanding of Wikipedia's role in a global information economy where
reliability is ever less certain, and source attribution ever more vital.
