Mauricio Rocha-e-Silva thought that he had spotted an easy way to raise the profiles of Brazilian journals. From 2009, he and several other editors published articles containing hundreds of references to papers in each others' journals-in order, he says, to elevate the journals' impact factors. Because each article avoided citing papers published by its own journal, the agreement flew under the radar of analyses that spot extremes in self-citation-until 19 June, when the pattern was discovered. Thomson Reuters, the firm that calculates and publishes the impact factor, revealed that it had designed a program to spot concentrated bursts of citations from one journal to another, a practice that it has dubbed citation stacking'.
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