  This paper investigates the stability of Twitter counts of scientific
publications over time. For this, we conducted an analysis of the availability
statuses of over 2.6 million Twitter mentions received by the 1,154 most
tweeted scientific publications recorded by Altmetric.com up to October 2017.
Results show that of the Twitter mentions for these highly tweeted
publications, about 14.3% have become unavailable by April 2019. Deletion of
tweets by users is the main reason for unavailability, followed by suspension
and protection of Twitter user accounts. This study proposes two measures for
describing the Twitter dissemination structures of publications: Degree of
Originality (i.e., the proportion of original tweets received by a paper) and
Degree of Concentration (i.e., the degree to which retweets concentrate on a
single original tweet). Twitter metrics of publications with relatively low
Degree of Originality and relatively high Degree of Concentration are observed
to be at greater risk of becoming unstable due to the potential disappearance
of their Twitter mentions. In light of these results, we emphasize the
importance of paying attention to the potential risk of unstable Twitter
counts, and the significance of identifying the different Twitter dissemination
structures when studying the Twitter metrics of scientific publications.
