Plus factors are economic actions and outcomes, above and beyond parallel conduct by oligopolistic firms, that are largely inconsistent with unilateral conduct but largely consistent with explicitly coordinated action. Possible plus factors are typically enumerated without any attempt to distinguish them in terms of a meaningful economic categorization or in terms of their probative strength for inferring collusion. In this article, we provide a taxonomy for plus factors as well as a methodology for ranking plus factors in terms of their strength for inferring explicit collusion, the strongest of which are referred to as "super plus factors."
William E. Kovacic, Robert C. Marshall, Leslie M. Marx, and Halbert L. White
Michigan Law Review