27 januari 2007
Why Scopus doesn't add substantially to the number of citations found in WoS
When performing citation analysis to measure research impact of scientists, we still rely on data retrieved from Web of Science. When we report our findings back to researchers they often come up with their citation figures from Google Scholar, which are sometimes, but not always, higher. So now and then figures from Scopus are quoted. The citations from Scopus are normally not that widely different from WoS, but only marginally different. It depends on science field a bit, but given the nearly double journal base for Scopus compared to WoS it comes as a surprise to some people.
How come we are asked?.
It is actually quite simple to explain. Garfield (1997) showed already that 2,000 journals of the Science Citation Index generated over 80% of all citations. Web of Science as a whole covers some 8,700 journals (interesting to sort out how many exactly, since this appears a disguised number as well). Scopus nearly doubles the journal base compared to WoS. But considering the fact that WoS already covers the most prestigious, important, cited journals, the doubling in journals only increases the total number of citations a wee bit.
Some subject specific databases such as SciFinder Scholar for chemistry, or PsychInfo for Psychology/Psychiatry will find more citations for journal articles on their domain since they have an even wider journal base on their domain than either WoS or Scopus.
I have tried to indicate this in the following figure.
The WoS square has a journal base of 8700 journals and attract in total a certain amount of citations. The journal base of Scopus is nearly double that of WoS, but not overlapping. The CAS (SciFinder Scholar) has a smaller partly overlapping database with WoS and Scholar, but (not properly indicated) a substantial number of journal are unique to CAS. On that smaller domain you are likely to find a few more citations.
I am not yet happy with the figure, but I hope it helps to illustrate this whole explanation.
Literature
Garfield, E. (1997). The significant scientific literature appears in a small core of journals. The Scientist 10(17): 13. http://www.garfield.library.upenn.edu/papers/currscience.html
How come we are asked?.
It is actually quite simple to explain. Garfield (1997) showed already that 2,000 journals of the Science Citation Index generated over 80% of all citations. Web of Science as a whole covers some 8,700 journals (interesting to sort out how many exactly, since this appears a disguised number as well). Scopus nearly doubles the journal base compared to WoS. But considering the fact that WoS already covers the most prestigious, important, cited journals, the doubling in journals only increases the total number of citations a wee bit.
Some subject specific databases such as SciFinder Scholar for chemistry, or PsychInfo for Psychology/Psychiatry will find more citations for journal articles on their domain since they have an even wider journal base on their domain than either WoS or Scopus.
I have tried to indicate this in the following figure.
The WoS square has a journal base of 8700 journals and attract in total a certain amount of citations. The journal base of Scopus is nearly double that of WoS, but not overlapping. The CAS (SciFinder Scholar) has a smaller partly overlapping database with WoS and Scholar, but (not properly indicated) a substantial number of journal are unique to CAS. On that smaller domain you are likely to find a few more citations.
I am not yet happy with the figure, but I hope it helps to illustrate this whole explanation.
Literature
Garfield, E. (1997). The significant scientific literature appears in a small core of journals. The Scientist 10(17): 13. http://www.garfield.library.upenn.edu/papers/currscience.html
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To me the hypothesis is partly self-fulfilling. It is the journal in WoS that are deemed unmissable by researchers and libraries and that easily findable and that gives articles therein a higher propensity to get cited.
# posted by 
: 30/1/07 13:59
: 30/1/07 13:59
@ Jeroen,
Only partly, even within WoS you are able to make clear distinctions etween the top and the rest. In Garfield's example it is probably the top 20 to 25% in journal titles, that Attract 80% of the citations. Pareto, Bradford, Diminishing returns, whatever.... A comon distribution in LIS. It works here as well.
Een reactie plaatsen
Only partly, even within WoS you are able to make clear distinctions etween the top and the rest. In Garfield's example it is probably the top 20 to 25% in journal titles, that Attract 80% of the citations. Pareto, Bradford, Diminishing returns, whatever.... A comon distribution in LIS. It works here as well.
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