  Fact checking by professionals is viewed as a vital defense in the fight
against misinformation.While fact checking is important and its impact has been
significant, fact checks could have limited visibility and may not reach the
intended audience, such as those deeply embedded in polarized communities.
Concerned citizens (i.e., the crowd), who are users of the platforms where
misinformation appears, can play a crucial role in disseminating fact-checking
information and in countering the spread of misinformation. To explore if this
is the case, we conduct a data-driven study of misinformation on the Twitter
platform, focusing on tweets related to the COVID-19 pandemic, analyzing the
spread of misinformation, professional fact checks, and the crowd response to
popular misleading claims about COVID-19. In this work, we curate a dataset of
false claims and statements that seek to challenge or refute them. We train a
classifier to create a novel dataset of 155,468 COVID-19-related tweets,
containing 33,237 false claims and 33,413 refuting arguments.Our findings show
that professional fact-checking tweets have limited volume and reach. In
contrast, we observe that the surge in misinformation tweets results in a quick
response and a corresponding increase in tweets that refute such
misinformation. More importantly, we find contrasting differences in the way
the crowd refutes tweets, some tweets appear to be opinions, while others
contain concrete evidence, such as a link to a reputed source. Our work
provides insights into how misinformation is organically countered in social
platforms by some of their users and the role they play in amplifying
professional fact checks.These insights could lead to development of tools and
mechanisms that can empower concerned citizens in combating misinformation. The
code and data can be found in
http://claws.cc.gatech.edu/covid_counter_misinformation.html.
