Google Scholar, Web of Science, and Scopus: A systematic comparison of citations in 252 subject categories

Abstract

Despite citation counts from Google Scholar (GS), Web of Science (WoS), and Scopus being widely consulted by researchers and sometimes used in research evaluations, there is no recent or systematic evidence about the differences between them. In response, this paper investigates 2,448,055 citations to 2,299 English-language highly-cited documents from 252 GS subject categories published in 2006, comparing GS, the WoS Core Collection, and Scopus. GS consistently found the largest percentage of citations across all areas (93%-96%), far ahead of Scopus (35%-77%) and WoS (27%-73%). GS found nearly all the WoS (95%) and Scopus (92%) citations. Most citations found only by GS were from non-journal sources (48%-65%), including theses, books, conference papers, and unpublished materials. Many were non-English (19%-38%), and they tended to be much less cited than citing sources that were also in Scopus or WoS. Despite the many unique GS citing sources, Spearman correlations between citation counts in GS and WoS or Scopus are high (0.78-0.99). They are lower in the Humanities, and lower between GS and WoS than between GS and Scopus. The results suggest that in all areas GS citation data is essentially a superset of WoS and Scopus, with substantial extra coverage.

Rising Atmospheric CO2 Lowers Concentrations of Plant Carotenoids Essential to Human Health: A Meta‐Analysis

“…To find relevant articles, we searched Google Scholar, which is “essentially a superset of WoS [Web of Science] and Scopus” citation data, for combinations of terms: carotenoid(s), carotene(s), xanthophyll(s), elevated carbon dioxide, and elevated CO 2 . Additional studies were found from references in the articles identified by the initial searches.…”

Japanese contributions to regional science

“…In general, GS displays a relatively more extensive coverage in the humanities and social sciences than WoS. The study by Martín-Martín et al (2018) found that in social sciences, the percentage of journal articles was 39%, and in the broad subject grouping of social sciences and business, economics and management, the proportion of unique GS citations which were not also in WoS surpassed 60%, although the scientific impact of these publications is much lower than those found by WoS. Therefore, a secondary objective of the current exercise is also to check whether in the interdisciplinary field of regional science GS can be seen as a reliable indicator for capturing the impact that each paper exerts on the wider academic community.…”

Conduct and reporting of citation searching in Cochrane systematic reviews: A cross‐sectional study

“…61 However, Google Scholar should not be dismissed as a useful tool, particularly for identifying grey literature, which has been estimated to comprise around half (48%-65%) of Google Scholar's content, including theses/dissertations, books and book chapters, conference proceedings, preprints, and reports, most of which are not indexed in Scopus or Web of Science. 62 This potentially makes Google Scholar particularly useful for identifying hard-to-find studies via citation searching, by combining a large amount of unique content with the aforementioned advantages of searching using citations. The use of multiple citation indexes can avoid some of the shortcomings of using one citation index; however, this approach was only reported in one review.…”