  The ever-increasing competitiveness in the academic publishing market
incentivizes journal editors to pursue higher impact factors. This translates
into journals becoming more selective, and, ultimately, into higher publication
standards. However, the fixation on higher impact factors leads some journals
to artificially boost impact factors through the coordinated effort of a
"citation cartel" of journals. "Citation cartel" behavior has become
increasingly common in recent years, with several instances being reported.
Here, we propose an algorithm -- named CIDRE -- to detect anomalous groups of
journals that exchange citations at excessively high rates when compared
against a null model that accounts for scientific communities and journal size.
CIDRE detects more than half of the journals suspended from Journal Citation
Reports due to anomalous citation behavior in the year of suspension or in
advance. Furthermore, CIDRE detects many new anomalous groups, where the impact
factors of the member journals are lifted substantially higher by the citations
from other member journals. We describe a number of such examples in detail and
discuss the implications of our findings with regard to the current academic
climate.
