'Special issue-ization' as a growth and revenue strategy: Reproduction by the "big five" and the risks for research integrity.

The exponential growth of MDPI and Frontiers over the last decade has been powered by their extensive use of special issues. The "special issue-ization" of journal publishing has been particularly associated with new publishers and seen as potentially "questionable." Through an extended case-study analysis of three journals owned by one of the "big five" commercial publishers, this paper explores the risks that this growing use of special issues presents to research integrity.