One great tool to explore the differing coverage of each indexer is
ShinyApp's Citation Overlap Visualizer.
You can specify by research area and subarea, and select up to three citation indexes to compare their coverage
in those areas. You can also leave the research area blank and compare overall coverage and size.
Credit: Much of this comparison was developed referencing the wonderful
Iowa State University Database Comparison Tool:
Those curious about additional comparison details or interested in learning more about any one particular database should go check it out!
The Web of Science Core Collection is a group of databases
(Science Citation Index Expanded, 1900-present; Social Sciences Citation Index, 1900-present;
Arts & Humanities Citation Index, 1975-present) that together cover more than 21,000 journals
across all disciplines. The Emerging Sources Citation Index (2005-present) tracks thousands of
additional journals that are being considered for inclusion in the main citation indexes.
Other files track references from conference proceedings (1990-present) and citations to books
(2005-present).
While a number of databases allow citation searching today, Web of Science
(now a product of Clarivate Analytics, formerly part of Thomson Reuters) was the original
citation index tool. It covers all disciplines, but is strongest in STEM subjects where
journals are the predominant form of cited literature.
The Web of Science platform currently also provides temporary access to
several databases that are not part of the Core Collection, including Biosis Citation Index,
Data Citation Index, and Zoological Record.
Quick Details:
- Size: 95+ million records; ~23 thousand journals; ~157 thousand books; ~11 million proceedings
- Scope: 1900-present;
focus is "journals of influence" which is typically interpreted as being the highest quality journals;
4% non-English language (with english abstract)
- lacks some types of cited literature (such as some books, white papers, dissertations, 'grey literature', journals not deemed high enough influence, etc)
- allows for mass export of citations
Scopus is an abstract and citation database. Abstracts provide brief synopses of publications, while
citations include key details such as authors, titles, and publication dates. Most Scopus citations
link directly to the full text, which can be accessed through various platforms. In addition to helping
identify experts, Scopus offers a wealth of research, metrics, and analytical tools across a wide range
of disciplines.
Quick Details
- Size: 100+ million records; ~28,000 active journal titles & ~15,000 inactive; ~300,000 books; ~12 million proceedings
- Scope: 1970 to present, with some older going back to 1788; covers more arts, humanities, and social sciences than Web of Science; 20% of records
are non-english (with english abstracts)
- covers more of arts, humanities, and social sciences than Web of Science
- owned by Elsevier, a major publisher, so may not be neutral in content inclusion decisions - though all content is subject to an independent review board
Google Scholar has easily the largest index of the three detailed here. This is because Google Scholar does not place the
same limits on content inclusion that either Web of Science or Scopus do, though it is not possible to know what exactly
is indexed in it, as it does not publish that information. What is known is that additional types of literature, including
grey literature, white papers, and other non-peer reviewed sources are included, as well as many more books than either of the
other two indexes contain, thanks to the large number of volumes ingested into google books. Because of its size and increased
scope, citation metrics taken from Google Scholar are often inflated compared to other indexers. For this reason, Google Scholar
is typically a better discovery and exploration tool than one made for extracting or analyzing any one person's citation metrics.
Quick Details
- size: ~400 million (estimated) records; unknown breakdown of how many of each type of record
- scope: largely unknown; contains more non-english language records than any of the other indexers; wider variety of record
types, including white papers, grey literature, theses, and more books than the other indexers listed here
- content quality can be poor; many non-peer reviewed records are indexed and counted in citation metrics
- extracting records or citations can be challenging - users have to manually copy/paste information they want
- authors need to create a profile for metrics to be easily reported on
