  In growing numbers, scholars are integrating social media tools like blogs,
Twitter, and Mendeley into their professional communications. The online,
public nature of these tools exposes and reifies scholarly processes once
hidden and ephemeral. Metrics based on this activities could inform broader,
faster measures of impact, complementing traditional citation metrics. This
study explores the properties of these social media-based metrics or
"altmetrics", sampling 24,331 articles published by the Public Library of
Science.
  We find that that different indicators vary greatly in activity. Around 5% of
sampled articles are cited in Wikipedia, while close to 80% have been included
in at least one Mendeley library. There is, however, an encouraging diversity;
a quarter of articles have nonzero data from five or more different sources.
Correlation and factor analysis suggest citation and altmetrics indicators
track related but distinct impacts, with neither able to describe the complete
picture of scholarly use alone. There are moderate correlations between
Mendeley and Web of Science citation, but many altmetric indicators seem to
measure impact mostly orthogonal to citation. Articles cluster in ways that
suggest five different impact "flavors", capturing impacts of different types
on different audiences; for instance, some articles may be heavily read and
saved by scholars but seldom cited. Together, these findings encourage more
research into altmetrics as complements to traditional citation measures.
