Publications without authorship information have been indexed as anonymous in the Web of Science database over the years. However, discussions on this subject have not been sufficiently addressed in the scholarly literature. Since bibliometrics studies are widely used for bibliometricians, scientific disciplines, science policy, and management, missing significant data as authorship metadata characterizes a gray zone that directly impacts these three components, and by extension, for bibliometrics and scientometrics. With a data collection performed at Web of Science Core Collection (WoSCC), 1,420,842 documents under "anonymous" authorship from 1900 to 2021 were retrieved, which accounted for 1.5% of the total documents indexed in the WoSCC. The publication data such as yearly growth of research publications, document type, language, productive research areas, and other bibliometric indicators were analyzed. The findings showed that in absolute numbers, a considerable growth of anonymous publications between 1996 and 2009, and there was a downward trend after that. However, this increase has not been proportional to the growth in the total number of publications indexed in the WoSCC. Articles, editorial materials, and news items were the top three document types among the WoSCC-indexed publications as anonymous. This study also finds two main scenarios of indexing publications as anonymous. The first is associated with the historical context of scholarly communication and practices that persist. The second is characterized by indexing persistent problems. This study suggests minimizing the error in databases, enabling an error-free indexing system and accurate bibliometrics studies.
Supplementary information: The online version contains supplementary material available at 10.1007/s11192-022-04494-4.
Keywords: Anonymous author; Indexing; Publications; Unknown author; Web of Science.
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