# CiteScore

CiteScore (CS) of an academic journal is a measure reflecting the yearly average number of citations to recent articles published in that journal. This journal evaluation metric was launched in December 2016 by Elsevier as an alternative to the generally used JCR impact factors (IFs). While CiteScore and JCR impact factor are similar in their definition, CiteScore is based on the citations recorded in the Scopus database rather than in JCR, and those citations are collected for articles published in the preceding three years instead of two or five.

## Calculation

In any given year, the CiteScore of a journal is the number of citations, received in that year, of articles published in that journal during the three preceding years, divided by the total number of "citable items" published in that journal during the three preceding years:[1]

${\displaystyle {\text{CS}}_{y}={{\text{Citations}}_{y-1}+{\text{Citations}}_{y-2}+{\text{Citations}}_{y-3} \over {\text{Publications}}_{y-1}+{\text{Publications}}_{y-2}+{\text{Publications}}_{y-3}}}$

For example, Nature had a CiteScore of 14.456 in 2017:

${\displaystyle {\text{CS}}_{2017}={{\text{Citations}}_{2016}+{\text{Citations}}_{2015}+{\text{Citations}}_{2014} \over {\text{Publications}}_{2016}+{\text{Publications}}_{2015}+{\text{Publications}}_{2014}}={114639 \over 7860}=14.59}$

Note that 2017 CiteScores are reported in 2018; they cannot be calculated until all of the 2017 publications have been processed by the indexing agency. CiteScores are typically released in late May,[2] approximately one month earlier than the JCR impact factors.[3] Scopus also provides the projected CiteScores for the next year, which are updated every month.[1]

## CiteScore vs. impact factor

CiteScore vs. IF for American Chemical Society (ACS, green) and Nature group journals (blue), 2017 data. The values for Nature journals lie well above the expected ca. 1:1 linear dependence because those journals contain a significant fraction of editorials.

CiteScore was designed to compete with the two-year JCR impact factor, which is currently the most widely used journal metric.[4][5] Their main differences are as follows:[6]

Parameter JCR IF CiteScore
Evaluation period (years) 2 3
Database JCR Scopus
No. indexed journals (2016) 11,000 22,000
Access Subscribers Anyone
Evaluated items Articles, reviews All publications

Another important difference is the definition of the "number of publications" or "citable items". While JCR excludes all kind of minor items, such as editorials, notes, corrigenda, retractions and discussions, all articles without exception are counted in CiteScore. The reason for such non-exclusion is that definition of "editorials" is vague and often questionable. As a result, CiteScore values are typically lower than the impact factor, because most editorial material receives much fewer citations than regular articles and reviews. For example, the journal Nature had an impact factor of 38.138, and a CiteScore of 14.38 in 2015, mostly because of a much larger denominator in CiteScore (7563) than in JCR IF (1722).[6]

## References

1. ^ a b Journal Metrics – FAQs. journalmetrics.scopus.com
2. ^ Elsevier releases 2017 CiteScore™ values. elsevier.com. 31 May 2018
3. ^ Journal Citation Reports 2018. clarivate.com. 26 June 2018
4. ^ Gray, Edward (2008). "Comparison of Journal Citation Reports and Scopus Impact Factors for Ecology and Environmental Sciences Journals". doi:10.5062/F4FF3Q9G. Cite journal requires |journal= (help)
5. ^ Journal Citation Reports: JCR. The University of Notre Dame Australia
6. ^ a b Van Noorden, Richard (2016). "Controversial impact factor gets a heavyweight rival". Nature. 540 (7633): 325–326. Bibcode:2016Natur.540..325V. doi:10.1038/nature.2016.21131. PMID 27974784.