Issues 17 October 2014

What is the impact of my article?

When assessing the impact of a published research article, it might seem logical to look at the Impact Factor of the journal that you find it in. But as journals and scholars have moved online, and citation indexing has been automated, the wealth of information for citation discovery and analysis has vastly increased.
Citation counts can tell a more accurate story about the scholarly impact that an individual article has made than the journal Impact Factor. But where should you look for these counts? There are a number of indexing services tracking and providing information about citations, each with advantages and disadvantages, spanning from bias to discipline-dependence, and limitations of the citation data source.

How these indexes differ is explained in more detail below.

Web of Science

An online subscription-based scientific citation indexing service maintained by Thomson Reuters. The coverage of the Web of Science encompasses over 30,000 scholarly books, 12,000 journals and 148,000 conference proceedings.

The selection is made on the basis of impact evaluations and comprise open-access journals, spanning multiple academic disciplines. However, Web of Science does not index all journals, and its coverage in some fields is less complete than in others. The total file count of the Web of Science was 46.1 million records, which included 727,549,189 cited references (September 5, 2009).


A collaborative reference linking service that functions as a sort of digital switchboard. It holds no full text content, but rather effects linkages through CrossRef Digital Object Identifiers (CrossRef DOI), which are tagged to article metadata supplied by the participating publishers.

PubMed Central

A free digital repository that archives publicly accessible full-text scholarly articles that have been published within the biomedical and life sciences journal literature. PMC contains over 2.9 million articles, with contributions coming directly from publishers or authors depositing their own manuscripts into the repository per the NIH Public Access Policy.
Submissions into PMC undergo an indexing and formatting procedure which results in enhanced metadata, medical ontologies, and unique identifiers. Content within PMC can easily be interlinked to many other NCBI databases and accessed via PubMed, where also the number of citations from articles in PMC are listed.

Google Scholar

A freely accessible web search engine that indexes the full text of scholarly literature across an array of publishing formats and disciplines; articles, theses, books, abstracts and court opinions, from academic publishers, professional societies, online repositories, universities and other web sites. Released in beta in November 2004, the Google Scholar index includes most peer-reviewed online journals of Europe and America's largest scholarly publishers, plus scholarly books and other non-peer reviewed journals.


Similar to Web of Science, an online subscription-based scientific citation indexing service maintained by Elsevier. Scopus holds 53 million records covering 21,915 titles across 5,000 publishers the largest abstract and citation database of peer-reviewed literature. Scopus delivers an overview of research output in the fields of science, technology, medicine, social sciences and arts and humanities.

Further reading

Also read a related article in the BioMed Central Blog, "The diverse world of citation indexing services".