The expansion of Google Scholar versus Web of Science: a longitudinal study
Web of Science (WoS) and Google Scholar (GS) are prominent citation services with distinct indexing mechanisms. Comprehensive knowledge about the growth patterns of these two citation services is lacking. We analyzed the development of citation counts in WoS and GS for two classic articles and 56 articles from diverse research fields, making a distinction between retroactive growth (i.e., the relative difference between citation counts up to mid-2005 measured in mid-2005 and citation counts up to mid-2005 measured in April 2013) and actual growth (i.e., the relative difference between citation counts up to mid-2005 measured in April 2013 and citation counts up to April 2013 measured in April 2013). One of the classic articles was used for a citation-by-citation analysis. Results showed that GS has substantially grown in a retroactive manner (median of 170 % across articles), especially for articles that initially had low citations counts in GS as compared to WoS. Retroactive growth of WoS was small, with a median of 2 % across articles. Actual growth percentages were moderately higher for GS than for WoS (medians of 54 vs. 41 %). The citation-by-citation analysis showed that the percentage of citations being unique in WoS was lower for more recent citations (6.8 % for citations from 1995 and later vs. 41 % for citations from before 1995), whereas the opposite was noted for GS (57 vs. 33 %). It is concluded that, since its inception, GS has shown substantial expansion, and that the majority of recent works indexed in WoS are now also retrievable via GS. A discussion is provided on quantity versus quality of citations, threats for WoS, weaknesses of GS, and implications for literature research and research evaluation.
KeywordsAutomatic indexing Citation classic Citation Index Historic trend Most highly cited paper Strengths and weaknesses
- Bakkalbasi, N., Bauer, K., Glover, J., & Wang, L. (2006). Three options for citation tracking: Google Scholar, Scopus and Web of Science. Biomedical Digital Libraries, 3(7).Google Scholar
- Bauer, K., & Bakkalbasi, N. (2005). An examination of citation counts in a new scholarly communication environment. D-Lib Magazine, 11(9).Google Scholar
- Beall, J. (2010). “Predatory” open-access scholarly publishers. The Charleston Advisor, 11(4), 10–17.Google Scholar
- Bornmann, L., Marx, W., Schier, H., Rahm, E., Thor, A., & Daniel, H.-D. (2009). Convergent validity of bibliometric Google Scholar data in the field of chemistry citation counts for papers that were accepted by Angewandte Chemie International Edition or rejected but published elsewhere, using Google Scholar, Science Citation Index, Scopus, and Chemical Abstracts. Journal of Informetrics, 3(1), 27–35.CrossRefGoogle Scholar
- Bosman, J., Van Mourik, I., Rasch, M., Sieverts, E., & Verhoeff, H. (2006). Scopus reviewed and compared: The coverage and functionality of the citation database Scopus, including comparisons with Web of Science and Google Scholar. Utrecht University Library. Retrieved April 2, 2013, from http://igitur-archive.library.uu.nl/DARLIN/2006-1220-200432/UUindex.html.
- Burright, M. (2006). Google Scholar: Science & technology. Issues in Science & Technology Librarianship, 45.Google Scholar
- Couto, F. M., Grego, T., Pesquita, C., & Verissimo, P. (2009). Handling self-citations using Google Scholar. International Journal of Scientometrics, Informetrics and Bibliometrics, 13(1). Retrieved June 30, 2013, from https://docs.di.fc.ul.pt/jspui/handle/10455/3304.
- Duncan, D. B. (1955). Multiple range and multiple F tests. Biometrics, 11(1), 1–42.Google Scholar
- García-Pérez, M. A. (2010). Accuracy and completeness of publication and citation records in the Web of Science, PsycINFO, and Google Scholar: A case study for the computation of h indices in psychology. Journal of the American Society for Information Science and Technology, 61(10), 2070–2085.CrossRefGoogle Scholar
- Garfield, E. (1974). Selecting the all-time citations classics. Here are the fifty most cited papers 1961–1972. Current Contents, 2, 5–8. Retrieved May 6, 2013, from http://garfield.library.upenn.edu/essays/v2p006y1974-76.pdf.
- Garfield, E. (1984). The 100 most-cited papers ever and how we select citation classics. Current Contents, 23, 3–9. Retrieved May 6, 2013, from http://www.garfield.library.upenn.edu/essays/v7p175y1984.pdf.
- Garfield, E. (1990). The most-cited papers of all time, SCI 1945–1988. Part 1A. The SCI top 100—will the Lowry method ever be obliterated? Current Contents, 7, 3–14. Retrieved May 6, 2013, from http://www.garfield.library.upenn.edu/essays/v13p045y1990.pdf.
- Garfield, E. (2005). The agony and the ecstasy—the history and meaning of the journal impact factor. Chicago: International Congress on Peer Review and Biomedical Publication. Retrieved May 6, 2013, from http://garfield.library.upenn.edu/papers/jifchicago2005.pdf.
- Google Scholar (2013). Inclusion guidelines for webmasters. Retrieved April 8, 2013 from http://scholar.google.com/intl/en/scholar/inclusion.html#overview.
- Harzing, A. W. (2008). Google Scholar—a new data source for citation analysis. University of Melbourne. Retrieved June 30, 2013, from http://www.harzing.com/pop_gs.htm.
- Harzing, A. W. (2013a). A longitudinal study of Google Scholar coverage between 2012 and 2013. Scientometrics. doi: 10.1007/s11192-013-0975-y.
- Hightower, C., & Caldwell, C. (2010). Shifting sands: Science researchers on Google Scholar, Web of Science, and PubMed, with implications for library collections budgets. Issues in Science and Technology Librarianship, 63.Google Scholar
- Jacsó, P. (2005b). As we may search—comparison of major features of the Web of Science, Scopus, and Google Scholar citation-based and citation-enhanced databases. Current Science, 89(9), 1537–1547.Google Scholar
- Jacsó, P. (2005c). Comparison and analysis of the citedness scores in Web of Science and Google Scholar. In Digital libraries: Implementing strategies and sharing experiences. Lecture Notes in Computer Science, vol. 3815 (pp. 360–369). Berlin, Heidelberg: Springer.Google Scholar
- Kresge, N., Simoni, R. D., & Hill, R. L. (2005). The most highly cited paper in publishing history: Protein determination by Oliver H. Lowry. The Journal of Biological Chemistry, 280(28), e25–e25.Google Scholar
- Labbe, C. (2010). Ike Antkare one of the great stars in the scientific firmament. ISSI Newsletter, 6(2), 48–52.Google Scholar
- López-Cózar, E. D., Robinson-García, N., & Torres-Salinas, D. (2012). Manipulating Google Scholar citations and Google Scholar metrics: Simple, easy and tempting. arXiv:1212.0638.Google Scholar
- Lowry, O. H., Rosebrough, N. J., Farr, A. L., & Randall, R. J. (1951). Protein measurement with the Folin phenol reagent. The Journal of Biological Chemistry, 193(1), 265–275.Google Scholar
- Noyori, R. (1992). Asymmetric catalysis by chiral metal complexes. ChemTech, 22(6), 360–367.Google Scholar
- Pauly, D., & Stergiou, K. I. (2005). Equivalence of results from two citation analyses: Thomson ISI’s Citation Index and Google’s Scholar service. Ethics in Science and Environmental Politics, 33–35.Google Scholar
- Pomerantz, J. (2006). Google Scholar and 100 percent availability of information. Information Technology and Libraries, 25(2), 52–56.Google Scholar
- Research Excellence Framework. (2013). Sub-panel 11: Citation data. Retrieved June 30, 2013, from http://www.ref.ac.uk/subguide/citationdata/googlescholar/.
- Sharma, V. (2008). Text book of bioinformatics. Meerut: Rastogi Publications.Google Scholar
- Thomson Reuters. (2013a). The Thomson Reuters journal selection process. Retrieved April 4, 2013, from http://thomsonreuters.com/products_services/science/free/essays/journal_selection_process/.
- Thomson Reuters. (2013b). Web of Science facts sheet. Retrieved April 29, 2013, from http://thomsonreuters.com/content/science/pdf/Web_of_Science_factsheet.pdf.
- Venter, J. C., Adams, M. D., Myers, E. W., Li, P. W., Mural, R. J., Sutton, G. G., & Beasley, E. (2001). The sequence of the human genome. Science, 291(5507), 1304–1351.Google Scholar
- Vine, R. (2006). Google Scholar. Journal of the Medical Library Association, 94(1), 97–99.Google Scholar
- Web of Knowledge. (2006). Retrieved April 29, 2013, from http://wokinfo.com/media/pdf/MostHighlyCitedArticles.pdf.
- Wleklinski, J. M. (2005). Studying Google Scholar: Wall to wall coverage? Online, 29(3), 22–26.Google Scholar