Metrics

The Journal Impact Factor is published each year by Clarivate Analytics. It is a measure of the number of times an average paper in a particular journal is cited during the preceding two years.

For example:

A = the number of times articles published in a specific journal in 2014 and 2015 were cited by journals during 2016.

B = the total number of 'citable items' published by that journal in 2014 and 2015. ('Citable items' are usually articles, reviews, proceedings, etc.; not editorials or letters-to-the-editor.)

2016 impact factor = A/B.

Actual value is intentionally only displayed for the most recent year. Earlier values are available in the Journal Citation Reports from Clarivate Analytics

CiteScore measures the average citations received per document published in a title. CiteScore values are based on citation counts in a range of four years (e.g. 2017-2020) to peer-reviewed documents (articles, reviews, conference papers, data papers and book chapters) published in the same four calendar years, divided by the number of these documents in these same four years (e.g. 2017-20).

For example, CiteScore 2020:

A = Citations to articles, reviews, conference papers, data papers and book chapters published in 2017-2020

B = Sum of articles, reviews, conference papers, data papers and book chapters published in 2017-2020

2020 CiteScore = A/B

A CiteScore is available for most active serial titles on Scopus - peer-reviewed journals, book series, conference proceedings and trade journals.

SCImago Journal Rank (SJR) is a measure of the number of times an average paper in a particular journal is cited, and as such is conceptually similar to the Impact Factor. A major difference is that instead of each citation being counted as one, as with the Impact Factor, the SCImago Journal Rank assigns each citation a value greater or less than 1.00 based on the rank of the citing journal. The weighting is calculated using a three-year window of measurement and uses the Scopus database. Authors can use these metrics when deciding where to publish.

The idea is to assign weights to bibliographic citations based on the importance of the journals that issued them. Citations issued by more important journals will be more valuable than those issued by less important ones. This 'importance' will be computed recursively, i.e., the important journals will be those which in turn receive many citations from other important journals.

Source-Normalized Impact per Paper (SNIP) measures contextual citation impact by weighting citations based on the total number of citations in a subject field. This unique perspective enables direct comparison of sources in different subject fields. The impact of a single citation is given higher value in subject areas where citations are less likely, and vice versa.

It is a ratio, with a numerator and a denominator. SNIP's numerator is a journal's impact per publication (IPP). This is simply the average number of citations received in a particular year (e.g. 2013) by papers published in the journal during the three preceding years (e.g. 2010, 2011 and 2012).

SNIP's denominator is the Database Citation Potential (DCP). We know that there are large differences between various scientific subfields in the frequency at which authors cite papers. In view of this, for each journal an indicator is calculated of the citation potential in the subject field it covers. This citation potential is included in SNIP's denominator, the DCP. SNIP is IPP divided by DCP.

SNIP enables direct comparison of sources in different subject fields. Citation potential is shown to vary not only between journal subject categories (groupings of journals sharing a research field) or disciplines (e.g., journals in Mathematics tend to have lower values than journals in Life Sciences), but also between journals within the same subject category. For instance, basic journals tend to show higher citation potentials than applied or clinical journals. Likewise, journals covering emerging topics tend to be higher than periodicals in classical subjects, or more general journals.

SNIP helps authors to identify which journals are performing best within their subject field, helping them decide where to publish. Mouse over the circles in the visualization and click on the year to view the journal's metrics. The size of the circles are compared to the highest values in the 5-year range. This highest value is represented by a closed circle, and the open circles indicate the journal's value compared to this highest value.