16.2 Data source comparisons: citations across disciplines
Three different data sources for citation analysis are investigated in this chapter:
- Thomson Reuters Web of Science: Generally known as ISI Web of Science or ISI. This is the traditional source of citation data, established by Eugene Garfield in the 1960s. Many universities still use this as their only source of citation data. It has complete coverage of citations in the more than 10,000 journals that are ISI listed, going back to 1900. It is generally updated once or twice a week. Although its worldwide coverage has been improving recently, it still has a North American bias in many disciplines. It charges commercial rates for access.
- Scopus: Introduced by Elsevier in 2004, Scopus aims to be the most comprehensive Scientific, Medical, Technical and Social Science abstract and citation database containing all relevant literature, irrespective of medium or commercial model. It covers nearly 18,000 titles from more than 5,000 publishers. It also claims worldwide coverage; more than half of Scopus content is said to originate from Europe, Latin America and the Asia Pacific region. It is updated daily and charges commercial rates for access.
- Google Scholar: Introduced by Google in 2004, Google Scholar has become a very popular alternative data source, not least through the fact that access is free and citation analysis programs such as Publish or Perish make bibliometric analysis easy. Some academics are skeptical about its wider coverage. However, studies (e.g. Vaughan and Shaw (2008) have found most of the citations to be scholarly. After a relatively slow start Google Scholar coverage is increasing, although Google still does not provide a list of its sources. Google Scholar is updated several times a week. For a more detailed analysis about Google Scholar as a source for citation analysis see Harzing & van der Wal (2008).
Table 1 reports the number of citations for our ten University of Melbourne professors. Definitions of data coverage of the citation data sources can be found underneath the table. As indicated above, most universities still use ISI as their primary or even only source of citation data. I will therefore first compare citation records for Scopus and Google Scholar with ISI citations records. Subsequently, I will compare the two different types of search functions in both ISI (General and Cited By search) and Scopus (General and More search).
Table 1: Number of citations for different disciplines using different data sources (May 2010)
|Field||ISI General Search||ISI Cited by Search||Scopus General Search||Scopus “More"||Google Scholar Author|
- ISI General search = citations IN ISI-listed journals TO publications ISI-listed journals.
- ISI Cited by search = citations IN ISI-listed journals TO all publications (incl. non ISI-listed journals, books, conference papers, white papers, government reports). Please note that even in the “cited by” search function ISI ignores citations for second and further authors for non-ISI publications.
- Scopus General search = citations IN Scopus-listed journals TO publications in Scopus-listed journals.
- Scopus More = citations IN Scopus-listed journals TO all publications (incl. non-Scopus listed journals, books, conference proceedings, white papers, government reports). Unlike the ISI Cited By search, the Scopus More search is not additive, i.e. in order to establish an academics total Scopus citations, one needs to add up the results from the Scopus General search and the Scopus More search.
- Google Scholar = citations IN all publications (incl. academic journals that are not ISI or Scopus listed, books, conference proceedings, white papers, government reports) TO all publications (incl. academic journals that are not ISI or Scopus listed, books, conference proceedings, white papers, government reports).