  To reflect the extent to which science is cited in policy documents, this
paper explores the presence of policy document citations for over 18 million
Web of Science-indexed publications published between 2010 and 2019. Enabled by
the policy document citation data provided by Overton, a searchable index of
policy documents worldwide, the results show that there are 3.9% of
publications in the dataset cited at least once by policy documents. Policy
document citations present a citation delay towards newly published
publications and show a stronger predominance to the document types of review
and article. Based on the Overton database, publications in the field of Social
Sciences and Humanities have the highest relative presence in policy document
citations, followed by Life and Earth Sciences and Biomedical and Health
Sciences. Our findings shed light not only on the impact of scientific
knowledge on the policy-making process, but also on the particular focus of
policy documents indexed by Overton on specific research areas.
