Skip to Main Content

Scholarly Metrics Journal Metrics

This guide will help you establish and maintain your professional identity and measure the impact of research outputs

There are multiple journal-level metrics. The most common is the Impact Factor. This guide describes impact factors and other journal metrics including SCImago, CiteScore and SNIP, based on citation data in Scopus, Google Scholar Metrics and Eigenfactor. It is important to keep in mind that all metrics have limitations and their value is context dependent.

Journal impact factor

A Journal impact factor is a quantitative measure based on the number of articles published per year relative to the number of citations to articles published in that journal. It is intended to reflect the importance of a particular journal in a field.

A journal's impact factor should not be the sole factor when evaluating the quality of the journal. In addition, journal metrics vary by discipline, with biomedical and related sciences skewing higher. Journal impact factor does not translate to the impact of the author or particular article within the journal, and they should not be used as a measure of a researcher's impact. 

How impact factors are calculated

A journal's impact factor for a given year is calculated by diving the number of citations in that year of articles published in the prior two years by the total number of articles published in the journal during that timeframe.

Factors that influence impact factor

It is important to keep in mind that the number of times a paper is cited is not a direct measurement of its quality. Impact factor may be skewed by the age of the journal/publisher, editorial policies, the types of articles published, and practices of self citation. For more meaningful results when comparing impact factors, it is best to compare within the same discipline as the impact factor can vary considerably across disciplines. Here are some other factors that may influence the impact factor:

  • Average Citation. It’s important to remember that the impact factor only looks at an average citation and that a journal may have a few highly cited papers that greatly increase its impact factor, while other papers in that same journal may not be cited at all.  Therefore, there is no direct correlation between an individual article’s citation frequency or quality and the journal impact factor.
  • Date of Publication. Because impact factor only looks at the citation frequency of articles from a journal in their first couple years of publication, journals with articles that are steadily cited for a long period of time rather than only immediately is not factored into the calculation and may negatively impact the journal's impact factor.
  • Large vs. Small Journals. Large and small journals are compared equally.  Large journals tend to have higher impact factors--nothing to do with their quality.
  • Review Articles. Impact factors are calculated using citations not only from research articles but also review articles (which tend to receive more citations), editorials, letters, meeting abstracts, and notes which may inflate the journal's impact factor compared to a journal that focuses primarily on research articles.
  • Changing / Growing Fields. Rapidly changing and growing fields (e.g. biochemistry and molecular biology) have much higher immediate citation rates, so those journals tend to have higher impact factors.

Database - Journal Citation Reports

Journal impact factors are published in Journal Citation Reports (JCR) a product of Thomson Reuters, via Web of Science. JCR provides more than the impact factor including total citations,  5-Year Impact Factor, open access statistics, the Eigenfactor Score and more. Below is a link to the database:

Eigenfactor

The value of the Eigenfactor is a complex impact factor score that takes into calculation the reputation of the citing journal. The Eigenfactor assigns weight to each earned citation, according to the "citedness" of the citing journal. Consider two journals: Journal A is highly cited; Journal B is poorly cited. Cites coming from Journal A are given greater weight when the Eigenfactors for other journals are being calculated and cites from Journal B are given less weight. Using these values, Eigenfactor can map the network of interactions between journals. More information on Eigenfactors.

Eigenfactor journal network map. Source: http://www.eigenfactor.org/projects/mappingScience/

Journal metrics by Scopus - SCImago

Scopus provides free access to journal-level metrics in Scimago Journal Rank (SJR) including CiteScore, percentile ranking, and Source Normalized Impact Per Paper (SNIP). SNIP measures contextual citation impact by weighting citations based on the total number of citations in a subject field. The impact of a single citation is given higher value in subject areas where citations are less likely, and vice versa. SNIP aims to allow direct comparison of sources in different subject fields. SNIP scores are derived from the Scopus abstract and indexing database and updated twice yearly.