CiteScore

In any given year, the CiteScore of a journal is the number of citations, received in that year and previous 3 years, for documents published in the journal during that period (four years), divided by the total number of published documents (articles, reviews, conference papers, book chapters, and data papers) in the journal during the same four-year period:[1]

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

For example, Nature had a CiteScore 2019[2] of 51.0

$${\displaystyle {\text{CS}}_{2019}={{\text{Citations}}_{2019}+{\text{Citations}}_{2018}+{\text{Citations}}_{2017}+{\text{Citations}}_{2016} \over {\text{Publications}}_{2019}+{\text{Publications}}_{2018}+{\text{Publications}}_{2017}+{\text{Publications}}_{2016}}={243894 \over 4786}=51.0}$$

Note that for example the 2017 CiteScores were reported first in 2018 when all data was available completely. CiteScores are typically released in late May,[3] approximately one month earlier than the JCR impact factors.[4] Note also the calculation date for each given CiteScore as later additions, corrections or deletions to the data will not lead to a score update.[5] Scopus also provides the projected CiteScores for the next year, which are updated every month.[1]

Old calculation

Before 2020 the score was calculated differently: In a given year, the CiteScore of a journal was 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]

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

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

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

Because the calculation method changed, knowing the calculation date is an important detail when comparing CiteScores. For example the Nature CiteScore in 2017, but calculated with the method of 2020, is 53.7.[6]

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.[7][8] Their main differences are as follows:[9]

Another difference is the definition of the "number of publications" or "citable items".[9]