Presentation at the 18th International Conference of the International Society for Scientometrics and Informetrics, July 12-15, 2021. Several initiatives have been taken to promote the openly availability of bibliographic metadata of scholarly publications in Crossref. We present an up-to-date overview of the availability of six metadata elements in Crossref: reference lists, abstracts, ORCIDs, author affiliations, funding information, and license information. Our analysis shows that the availability of these metadata elements has improved over time. However, it also shows that many publishers need to make additional efforts to realize full openness of bibliographic metadata. To illustrate the value of open metadata, we use the metadata in Crossref to construct and visualize a large citation network of scholarly journals.

1. Crossref as a source of open bibliographic
metadata
Nees Jan van Eck and Ludo Waltman
Centre for Science and Technology Studies (CWTS), Leiden University
18th International Conference on Scientometrics & Informetrics
Leuven, Belgium, July 12-15, 2021

2. Introduction
• Crossref is becoming an increasingly interesting data
source for bibliometric analyses
• Several initiatives have been taken to promote the open
availability of bibliographic metadata of scholarly
publications in Crossref:
– Initiative for Open Citations (launched in 2017)
– Initiative for Open Abstracts (launched in 2020)
• There are still many publications in Crossref for which
important metadata elements are missing
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3. Aim
• We present an up-to-date overview of the availability of bibliographic
metadata in Crossref, focusing on six metadata elements:
– reference lists
– abstracts
– ORCIDs
– author affiliations
– funding information
– license information
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4. Data
• Crossref’s XML Metadata Plus Snapshot
(downloaded on March 5, 2021)
• 86.4 million records classified as
journal article:
– 2000-2020: 52.8 million journal articles
– 2019-2020: 8.8 million journal articles
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5. Yearly number of journal articles
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6. Increasing availability of metadata over time
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7. Publisher analysis (2019-2020)
• For the 8.8 million journal articles in Crossref in 2019 and 2020, we
determined for each publisher the percentage of articles that have:
• an openly available reference list
• an abstract
• at least one ORCID
• at least one author affiliation
• funding information
• license information
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8. Publisher analysis (2019-2020): References
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9. Publisher analysis (2019-2020): Abstracts
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10. Publisher analysis (2019-2020): ORCIDs
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11. Publisher analysis (2019-2020): Affiliations
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12. Publisher analysis (2019-2020): Funding information
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13. Publisher analysis (2019-2020): License information
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14. Visualizing a journal citation network
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86.4 million journal articles
1.32 billion references
0.94 billion citation links with
other journal articles
Interactive version: https://bit.ly/3dNHA2A

15. Conclusions
• Open bibliographic metadata helps:
– to make bibliometric analyses more transparent, reproducible, and inclusive
– to make it easier to find the most relevant scholarly literature
• Open availability of different metadata elements in Crossref has
improved over time
• Many publishers need to make additional efforts to realize full
openness of bibliographic metadata:
– publishers often do a good job in making certain metadata elements openly
available, but they fail to do the same for other metadata elements
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16. Future research
• Calculate more detailed statistics
• Examine other content types:
– conference papers
– book chapters
– preprints
– data sets
– peer review reports
• Analyze links between journal articles and other content types
(e.g., preprints, data sets, peer review reports)
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17. ecknjpvan@cwts.leidenuniv.nl
@neesjanvaneck
www.cwts.nl/people/neesjanvaneck
Thank you
for your attention!