Scientometrics are increasingly used to evaluate scientists for positions, etc. Some while ago, citation numbers for individuals (and derived parameters, such as the h-index) could only be obtained via Thomson Reuters  ISI Web of Science. Then came Elsevier’s Scopus, and now we also have Google Scholar Citations. Most reseachers use them without much thinking about them, and quite often without referencing the specific source they used to obtain their personal metrics. However, the citation counts and h-indices calculated by these 3 services may be very different.

I illustrate this with my own metrics. Scopus finds  15528 total citations , with 1672 counts for the highest cited article (‘Pathobiology of stroke’) , and an h-index of 65. For Google Scholar Citations the corresponding numbers are  total citations 20879, highest cited article (‘Pathobiology of stroke’) 2268 ,and an h-index 73. Web of Science on the other hands yields 14391 total citations , highest cited article (‘Pathobiology of stroke’) 1332, an  h-index 64.

Scopus

Total citations 15528, highest cited article (‘Pathobiology of stroke’) 1672, h-index 65

Google Scholar Citations

Total citations 20879, highest cited article (‘Pathobiology of stroke’) 2268 , h-index 73

Web of Science (Thomson Reuters)

Total citations 14391, highest cited article (‘Pathobiology of stroke’) 1332, h-index 64

See also Bar-Ilan J. Which h-index?  A comparison of WoS, Scopus, and Google Scholar. Scientometrics (2008) 74:257-271. They found no systematic relationship between the three services, such that Google would always return higher numbers, etc.

The differences of course are caused by different source materials which is indexed, different indexing periods,  and idiosyncrasies and flaws of the search algorithms.  Bottom line:

1) Scientists need to indicate how they have obtained the metrics.

2) Metrics of scientists can only be compared when the come from the same source.