51 academic journals were excluded from Thomson Reuters' research impact factor ranking 2011. On annual basis, journals that attempt to significantly climb ranks through self-citation are banned for a couple of years. This year, 28 new offenders were subject to this measure. In 2007, this was only the case for 9 journals.
By comparison, this number is still relatively small given that Thomson Reuters includes more than 10,500 periodicals in its ranking. However, one case of systematic manipulation stands out. Three months ago Scholarly Kitchen revealed that The Scientific World Journal, Cell Transplantation and Medical Science Monitor had used mutual citations to artificially boost their research impact standing.
Defining whether "anomalous citation patterns" are in fact questionable for the science community is difficult, as a recent blog by Nature magazine argues. Thomson Reuters itself only investigates cases where self-citation leads to significant boosts of the impact factor.