This week, Physics Today published an article on the Journal Impact Factor and the new CiteScore index. Both are average citation values within a certain year to papers published in a few preceding years. The main difference between the two are that the JIF uses citations to papers in the prior two years while CiteScore includes citations to papers in the previous three years. The other main difference is that Elsevier, the creator of the new CiteScore index, is making everything about the creation of the values open, while Thomson Reuters only makes the formula and numbers used available to subscribers, and the actual list of citations is kept proprietary.
As the Physics Today article notes, the values are similar for most journals between the two indices, but some shifting is evident, especially among the top titles. For JGR (all sections combined), the values are almost identical, with the 2015 Impact Factor being 3.32 and the CiteScore being 3.39 (to two significant digits, which I don’t like to do).
Also as noted in the Physics Today article, the similarity in how they are calculated suggests that the complaints about JIF are largely applicable to CiteScore. Okay, it includes another year, but Thomson Reuters already produces a 5-year Impact Factor, so CiteScore splits the difference. Both are susceptible to the size of the “highly cited tail” of the paper distribution in a journal, especially if the number of citable items is relatively small. Also, both are susceptible to manipulation, if publishers were to unethically push authors of new manuscripts into citing papers in their journals.
I find it bewildering that there are ~5% of journals in existence with a CiteScore of zero (as reported in the Physics Today article). This means that there was a year in which there were no citations to any of the articles published in that journal for the prior three years. I have not looked up the names of these journals to look for a trend or commonality but, regardless…wow. Thanks again for reading and citing the papers in JGR Space Physics!