Abstract
We study how a single paper affects the impact factor (IF) of a journal by analyzing data from 3,088,511 papers published in 11639 journals in the 2017 Journal Citation Reports of Clarivate Analytics. We find that IFs are highly volatile. For example, the top-cited paper of 381 journals caused their IF to increase by more than 0.5 points, while for 818 journals the relative increase exceeded 25%. One in 10 journals had their IF boosted by more than 50% by their top three cited papers. Because the single-paper effect on the IF is inversely proportional to journal size, small journals are rewarded much more strongly than large journals for a highly cited paper, while they are penalized more for a low-cited paper, especially if their IF is high. This skewed reward mechanism incentivizes high-IF journals to stay small to remain competitive in rankings. We discuss the implications for breakthrough papers appearing in prestigious journals. We question the reliability of IF rankings given the high IF sensitivity to a few papers that affects thousands of journals.
Highlights
AND MOTIVATIONThe effect of a journal’s scale on its citation average cannot be overstated
We study how a single paper affects the impact factor (IF) of a journal by analyzing data from 3,088,511 papers published in 11639 journals in the 2017 Journal Citation Reports of Clarivate Analytics
Because the single-paper effect on the IF is inversely proportional to journal size, small journals are rewarded much more strongly than large journals for a highly cited paper, while they are penalized more for a low-cited paper, especially if their IF is high
Summary
AND MOTIVATIONThe effect of a journal’s scale (i.e., size) on its citation average cannot be overstated. While actual journals are not completely random, the Central Limit Theorem explains to a large extent their IF scale behavior, and allows us to understand how the balance in IF rankings is tipped in two important ways: (a) Only small journals can score a high IF; and (b) large journals have IFs that asymptotically approach the global citation average as their size increases, via regression to the mean. At a less quantitative level, the scale dependence of citation averages has been noted earlier, by Amin and Mabe (2004), Campbell (2008), and Antonoyiannakis and Mitra (2009). It is almost always neglected in practice. IFs for journals of all sizes are lumped together in rankings such as the Journal Citation Reports ( JCR) or the Impact Factor Quartile rankings of Clarivate
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