  Science is a cumulative activity, which can manifest itself through the act
of citing. Citations are also central to research evaluation, thus creating
incentives for researchers to cite their own work. Using a dataset containing
more than 63 million articles and 51 million disambiguated authors, this paper
examines the relative importance of self-citations and self-references in the
scholarly communication landscape, their relationship with the age and gender
of authors, as well as their effects on various research evaluation indicators.
Results show that self-citations and self-references evolve in different
directions throughout researchers' careers, and that men and older researchers
are more likely to self-cite. Although self-citations have, on average, a small
to moderate effect on author's citation rates, they highly inflate citations
for a subset of researchers. Comparison of the abstracts of cited and citing
papers to assess the relatedness of different types of citations shows that
self-citations are more similar to each other than other types of citations,
and therefore more relevant. However, researchers that self-reference more tend
to include less relevant citations. The paper concludes with a discussion of
the role of self-citations in scholarly communication.
