The most cited documents in Google Scholar & Web of Science: two sides of the same coin

As one more example of those unlikely but still curiously recurrent cases of two different teams simultaneously studying the same research problem, two studies on highly cited documents have been released this week with barely a few hours of difference between them. One of them was published by Van Noorden, Maher & Nuzzo in Nature. The other one was submitted by Martín, Ayllón, Orduña & Delgado López-Cózar to the arXiv repository.

The first one studies the top 100 most cited articles in Web of Science on the ocassion of the 50^th anniversary of the Science Citation Index (SCI), although it also offers an alternative list containing the top 100 most cited documents in Google Scholar. Additionally, the authors comment many of these articles individually and their contribution to the advancement of science.

Conversely, the second study, carried out in the ocassion of Google Scholar's 10^th anniversary,  takes a different approach to the same issue, analysing the highly cited documents in Google Scholar (a sample of 64,000 documents published between 1950 and 2013). Among other things, we compare the ranking obtained from Google Scholar data to the most cited documents in Web of Science.

This unique event has an interesting side effect, since it allows us to compare and verify the validity of the methodologies used and the results reached in both studies.

Our conclusion is that Google Scholar presents a different view to the one we were used to after many years using the Web of Science (50% of the highly cited documents in GS are not indexed in WoS). 

However, if we analyse only those documents that are indexed both in Google Scholar and the Web of Science (32,680 documents in our sample), Google Scholar presents a very similar portrait of the world of research to the one offered in Web of Science, with a significant difference: 91.6% of the documents have received more citations in GS than in WoS. Only 3,079 documents (9.4%) have more citations according to WoS than in GS. Furthermore, the average number of citations per document in GS is 1.79, and 1.08 in WoS, which means that on average, GS has 70% more citations per document than WoS.

Our recommendation: read, and compare