1. Citation counts: a brief comparison of Google Scholar, Web of Knowledge and Scopus

2. How can I find the number of times a work has been cited by other authors?
ISI Web of Knowledge
Google Scholar
Scopus
Also:
Full text databases, for example, Abi Inform
Specialist websites – for example, Citeseer (computing)
Web citations

3. How do they compare?
Google Scholar often returns higher numbers, as it may also include conference papers, books, book chapters and dissertations, whereas Web of Knowledge and Scopus will return mostly journal articles.
However, Google Scholar results in particular need to be followed through and checked. Also, it will probably take longer to extract the information from Google Scholar.
Sources on Scopus and Web of Knowledge are more easily verified and references downloaded.
Scopus is focussed on Science and Social Science, although some Humanities literature is also included.

4. When searching, take into account…
Misspellings.
Incorrect citations (for example, year, volume number, inconsistencies of abbreviation).
Author order – may only be cited by the first author.
Self-citations.
Monographic literature is not well covered.

5. Sample search: biomedical journal article (2004), search undertaken Dec Results show overlap between the three databases.
Total number of cited references=69

6. Sample search: humanities journal article (2001), search undertaken Dec Results show overlap between the three databases.
Total number of cited references=33

7. Summary
Counting citations can be a lengthy process – it will take some time and checking to get a definitive list.
Google Scholar results especially need to be followed up to take into account dead links, duplicates, and the time taken to verify quality if the link is to an intranet or in a language other than your own.
However, Google Scholar may pick up on a wider range of international publications which will help to show impact.
Use all options and collate the results.

8. Further reading
Bakkalbasi, N. et al Three options for citation tracking: Google Scholar, Scopus and Web of Science. Biomedical Digital Libraries [online], 3(7). Available at: <URL: [Accessed: 17 November 2006].
Bar-Ilan, J An ego-centric citation analysis of the works of Michael O. Rabin based on multiple citation indexes. Information Processing and Management [online], 42. Available at: <URL: > [Accessed: 23 November 2006].
Jacso, P Deflated, inflated and phantom citation counts. Online Information Review [online], 30(3). Available at: <URL: [Accessed: 17 November 2006].
Nisonger, T. E Citation Autobiography: An Investigation of ISI Database Coverage in Determining Author Citedness. College & Research Libraries [online], 65(2). Available at: <URL: [Accessed: 23 November 2006].
Vaughan, L. and Shaw, D Web citation data for impact assessment: A comparison of four science disciplines. Journal of the American Society for Information Science & Technology [online], 56(10). Available at: <URL: [Accessed: 24 November 2006].