  Data collected by social media platforms have recently been introduced as a
new source for indicators to help measure the impact of scholarly research in
ways that are complementary to traditional citation-based indicators. Data
generated from social media activities related to scholarly content can be used
to reflect broad types of impact. This paper aims to provide systematic
evidence regarding how often Twitter is used to diffuse journal articles in the
biomedical and life sciences. The analysis is based on a set of 1.4 million
documents covered by both PubMed and Web of Science (WoS) and published between
2010 and 2012. The number of tweets containing links to these documents was
analyzed to evaluate the degree to which certain journals, disciplines, and
specialties were represented on Twitter. It is shown that, with less than 10%
of PubMed articles mentioned on Twitter, its uptake is low in general. The
relationship between tweets and WoS citations was examined for each document at
the level of journals and specialties. The results show that tweeting behavior
varies between journals and specialties and correlations between tweets and
citations are low, implying that impact metrics based on tweets are different
from those based on citations. A framework utilizing the coverage of articles
and the correlation between Twitter mentions and citations is proposed to
facilitate the evaluation of novel social-media based metrics and to shed light
on the question in how far the number of tweets is a valid metric to measure
research impact.
