Citation search


Bauer et al have published two articles on citation search:Bakkalbasi N, Bauer K, Glover J, Wang L (2006)
Three options for citation tracking: Google Scholar, Scopus and Web of Science Biomedical Digital Libraries, Vol. 3, No. 7, 29 June.

Bauer K and Bakkalbasi N (2005) An Examination of Citation Counts in a New Scholarly Communication Environment
D-Lib Magazine, Vol. 11, No. 9.

Noruzi also made some brief evaluations in an article:

Noruzi, Alireza Google Scholar: The New Generation of Citation Indexes
LIBRI Vol. 55, Iss. 4, p. 170-80
Belew K compared citation search in WoS and Google Scholar:

Belew, RK (2005) Scientific impact quantity and quality: [PDF] Analysis of two sources of bibliographic data.
Arxiv.org

The first article of Bauer and Bakkalbasi showed the citation count for GS was higher than WoS and Scopus for 2000. But for 1985 WoS seem to be best to cover citations. Comparing WoS and Scopus, WoS found more citations for 1985 but for 2000 it was similar.

The next article of Bauer, Bakkalbasi et al evaluated journal articles from two disciplines: oncology and condensed matter physics (CM physics) and two years: 1993 and 2003.

Their conclusion is:”This study did not identify any one of the three tools studied to be the answer to all citation tracking needs”. Scopus shows strength for oncology articles from 2003, but WoS performed better for CM physics and was better for both disciplines published in 1993. GS returned smaller number but had a large set of unique citing material for 2003. Bauer, Bakkalbasi et al make clear:”…it is clear that Google Scholar provides unique citing material.”

The article by Belew compares GS with WoS by author search. Belew randomly selected six academics from same interdisciplinary department and bibliographies of all publications by these authors were manually reconciled against 203 references found by one or both systems. WoS discovered 4741 citations and GS 4045, but when evaluating each author 2 authors get significantly more citations in GS.

Belew indicates that because of the quality in some bibliographic citations it’s common to find that same publication has been treated as more than one record. When searching cited ref search in WoS for an author you can find these types of errors. As Belew indicates in Table 1. With these types of errors it’s possible to loose citations for an article in WoS, but instead there are sometimes duplicates of an article (preprint and original article) that inflates citation count. Belew does not discuss that GS often shows duplicates and sometimes if you manually check the number of times cited it’s incorrect displayed.

Belew conclusion is: “GS seems competitive in terms of coverage for materials published in the last twenty years; before then WoS seems to dominate”.

We also earlier this year made a small test between Scopus and WoS by searching author name, but just author names that we can sort out as unique.

Noruzi made free text searches when testing citation search with search statement: webometrics OR webometric. Freetext search is not a proper subject search. As Bauer et al is pointing out WoS, GS and Scopus databases processes a freetext search in different ways. For example Google Scholar indexes even the fulltext of articles in contrary to WoS and Scopus. Though in this case Noruzi still have just compared each known article, though the method of choosing articles and the low amount of articles may be arguable.

None of Belew and Bauer et al have discussed the problems with citation counting in Google Scholar. Though Peter Jacso have criticized Bauer et al and presented examples of flaws in Google Scholar:

Jacso, Peter ([2005b]) Google Scholar and The Scientist
(Published on university homesite as extra material). [online] http://www2.hawaii.edu/~jacso/extra/gs/
I believe the percentage of flaws in Google Scholar may not decrease the value of the findings significantly of Belew and Bauer et al but it should be considered and discussed. Research on the propotions of citation counting flaws in Google Scholar would be of considerable value for future evaluations.

I checked the citation counting in Google Scholar of the first article Noruzi refers to in his test in Table 2:

C Almind and P. Ingwersen Informetric analyses on the world wide web Journal of Documentation Vol. 54 Iss. 4, p. 404-426

Check tihis screenshot:

I received 4 hits where the first hit clusters 11 duplicates (look at link group of 11). 3 duplicates (hit 2-4) are unclustered. Together it’s 192 citations for the article of Almind et al. But if you check the reliance of citations in all hits you will find duplicates. I evaluated maually all 192 citations together and found 13 obvious duplicates. It’s manually checked and some more duplicates may be found. All records in chinese letters are not checked. Here are screenshots on all duplicates put together with an image editing software:

Of 192 citations from GS, 12 is duplicates which gives these results: GS 180, WoS 90. This means 6% is incorrect citations.

Of course WoS could have duplicates also.

Conclusion: Scopus is important for finding more citations from 1996 and current. Google Scholar is important because it finds a lot of unique citations but each reference with information on times cited should be manually checked by counting and looking for duplicates. Web of Science is still competetive, especially for older material.

As Noruzi mention in his article GS indexes a lot more of publication types and from various languages. If every citation, no matter from which source, has the same value of 100%, GS is an important source. The discussion should exceed on the value of each citation. Should self-citation get any value at all? Should articles not peer-reviewed get a lower value for their citations?

When searching this article An Examination of Citation Counts in a New Scholarly Communication Environment by K Bauer, N Bakkalbasi – D-Lib Magazine, 2005 in Google Scholar you get the result cited by 8 other papers:


When checking all this 8 papers cited the Bauer et al article you well get three citations from the same source in The Scientist “The future of citation analysis”:

Google Scholar have managed to find 4 duplicates (as you can see in the last reference in link “group of 4″) and cluster them but missed two other duplicates.

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.

In several of his writings, Peter Jacso has indicated the inconsistencies of Google Scholar. One important flaw is the citation search. Both his web published paper "Google Scolar and The scientist" and the article "As we may search" published in Current Science 2005 (please see References to literature) discuss the problems.

My testings indicates less inconsistencies than before, but still they exist. 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 comparisions of the average number of times an article is cited. They checked the citation frequency of each article for a certain year, in this case both 1985 and 2000, in the Journal of the American Society for Information Science and Technology (JASIST). The search for 2000 showed Google Scholar had 4.5 more citations than Web of Science and 3.9 more citations than Scopus. But searching 1985 Web of Science had 8.7 more citations than Google Scholar and Google Scholar had "just" 2.9 more citations than Scopus. The major shortcoming in this article is that they never analyzed the inconsistencies with Google Scholar citation Search. The citation count doesn't always work properly. Here's an example of a record that indicates Cited by 15 (other sources):

When clicking this link Cited by 15 you will find only 14 citations:

Here's another example of an article by P Jacso himself. Cited by 3 sources according to Google Scholar:

When clicking this link Cited by 3 you will find only 2 citations:

This search on semiconductors is an example from Jacso. In this reference it seems like the article is published 2006, but checking the source shows it's published 1990 and 2006 is the starting page of the article:

Jacso has also pointed out the flaws of duplication in his article "As we may search" in Current Science. Google Scholar works hard with the ability to cluster duplicate articles together. If you look at the preceding screenshot after the title you see the link group of 3>>. Clicking that link shows you 3 duplicates. Because Google Scholar indexes not just peer-reviewed journal articles, but preprint archives, conference papers, master thesis, webpublished materials etc you understand they have a hard problem to discover duplicates.

Here's an example. Searching sojka modeling drop size distributions gives as the first hit an article by Bainsky and Sojka with title "Modeling drop size distributions". That article should be Cited by 7 other sources according to Google Scholar.

By clicking Cited by 7 you find 7 hits but two of them are duplicates. View the two titles "Modeling Spray Impingement using Linear Stability Theories for Droplet Shattering". Though the first title has a link to group of 2>>.

Conclusion: Don't trust the Google Scholar citation counting without manually checking it for inconsistencies in terms of counting and clustering duplicates.

A very common problem in citation search is incorrectly cited references in journal articles, in most cases due to the careless attitudes of authors and even careless journal editors. Librarians often meet carelessly written cited references in daily work and that often makes the retrieval of an article very problematic and ineffective.

But it’s not just a problem when locating items. It’s an even worse problem for the citation databases that use these cited references to count times cited for a journal article. That’s why you should use the Cited reference search when searching all cited references for a journal article in Web of Science.

We checked 2 incorrectly cited references in Web of Science and then checked if it was an author error or a database indexing error by checking up the original journal article. Then we checked if they were corrected in Scopus. Here’s the first example when searching author Aasa A in Web of Science:


The page is incorrect in cited reference 2. It’s page 644 but should be page 664. We checked the citing article as follows:

Checking the same incorrect cited reference in the reference list of the article based on how it’s indexed by Web of Science:

The original article has the incorrect page 644, which should be page 664:

Checking up the same article in Scopus shows the cited reference is correct and must have been corrected by Scopus (or being corrected in the database where the reference is collected from):

Checking up the author Elgh F via Cited Reference Search in Web of Science gives 3 incorrectly cited references with IN PRESS in front of the journal abbreviation:

We checked the two citing articles for one of the incorrectly cited references IN PRESS J VIROL MET:

Checking the cited references of the first citing journal article in Web of Science:

Then we checked the original article and found out that the cited reference is written with the words in press after the journal title J. Virol. Methods. and the in press message should not have been interpreted as a part of the journal title in Web of Science and especially not with in press in front of the journal title.

So let’s check Scopus? It’s correct. In press follows after and separately from the journal title.

As you may also have seen Scopus has 6 cites to the Aasa U article and 33 cites to the Elgh F article. Comparable to Web of Science with 4 cites (5 if you include the incorrect one) to the Aasa U article and 33 cites to the Elgh F article.

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