“this year the editorial integrity team at Clarivate identified a new type of anomalous citation behavior: self-stacking. This is where the journal contains one or more documents with citations that are highly concentrated to the JIF numerator of the title itself. This is the first year we have formally defined the criteria for self-stacking suppression, and as such we have made the decision to issue a warning to six journals rather than suppress the journal’s JIF. Going forward, continued journal self-stacking will result in suppression of JIF”
However, contrary to what Clarivate now says, it is not a new anomalous citation, as it had already been identified in 2016 by Heneberg and he even wrote at the time that Thomson Reuters (the firm that was later bought by Clarivate) had no way of detecting this manipulation: “Thomson Reuters currently does not have any algorithm to detect citation stacking”
The impact factor is a registered trademark of Clarivate Analytics that has been denounced for the damage it has brought to science. And that is why many scientists have written that it is a metric that should never be used in the evaluation of researchers (or research units). It should be borne in mind that it is sufficient for a journal to have a high rejection rate, giving preference to articles by highly-cited authors in top universities for this fact alone to contribute to an increase in the impact factor. https://pacheco-torgal.blogspot.com/2021/03/desk-rejectionthe-editor-manuscript-game.html
PS – Clarivate Analytics itself warns against the use of the impact factor in the evaluation of researchers: “In the case of academic evaluation for tenure, it is inappropriate to use the impact of the source journal to estimate the expected frequency of a recently published article”
Pacheco-Torgal 