We made some citation frequency comparisons between Scopus, Web of Science and Google Scholar. As Scopus counts citations from 1996 we limited the comparisions to articles published from 1996 and current. The result of the figures in the screenshot showed:

Scopus finds 9% more citations than Web of Science when limited to articles from 1996-.

Scopus finds 20% more citations than Google Scholar when limited to articles from 1996-.

Web of Science finds 10% more citations than Google Scholar when limited to articles from 1996-.

Important to know is that Web of Science indexes more than 9,000 journals compared to Scopus 15,000 journals, though Web of Science argues that (according to Bradford's Law) they have the core journals which have the most citations. Google Scholar has no list of journals and other sources they index, but they index both articles from the proprietary web and scholarly archives, master theses, books etc. Google Scholar citation counting is not working properly either as we already pointed out in a previous posting. In this test all cited references from Scopus haven't been retrieved, just the indexed articles.

As we also already mentioned, the article "An Examination of Citation Counts in a New Scholarly Communication Environment" published in D-Lib magazine September 2005 Vol. 11, No. 9. by Kathleen Bauer et al at Yale University Library made some citation counting. But when we just counted all citations for a random 5 set of authors at Umeå university, Bauer et al made comparisons of the average number of times an article is cited. Both our test and the test by Bauer et al didn't check the Google Scholar inconsistencies of citations counting and duplicates.

Some of the findings from the article by Bauer et al follow below. The information derives from the tables in their article.

The search for articles published 2000 in Journal of the American Society for Information Science and Technology (JASIST) showed for example:

Web of Science counts 0.3 more citations than Scopus.

The search for articles published 1985 in Journal of the American Society for Information Science and Technology (JASIST) showed for example:

Web of Science counts 11.9 more citations than Scopus.

Because Scopus just count citations from articles published from 1996 and current the 11.9 difference is not surprising. Though the 0.3 difference for articles published from 2000 is more questionable. This test by Bauer et al has its limitations because it's limited to just one journal (i.e., JASIST).

Conclusion: Different testing methods at least shows that Scopus definitely is important when searching citations for articles published from 1996. Due to inconsistencies in Google Scholar its not suggested as a single usable tool for citation search.