William & Mary Law Review


Most price-fixing litigation turns on whether the plaintiffs can present sufficient circumstantial evidence from which a reasonable jury could infer that the defendants did, in fact, conspire to raise prices. This generally entails the proffering of plus factors, a type of evidence that suggests parallel conduct by the defendants was the product of collusion, not independent decisions. As their name suggests, plus factors are just that—factors. Proving a collection of factors may be necessary for a plaintiff’s case, but no individual factor is ever required. If it were, it wouldn’t be a factor; it would be an element.

Several federal courts, however, have improperly converted some aspects of antitrust law’s factor test into an element test, which raises the plaintiff’s evidentiary burdens in a way that protects price-fixing conspiracies from antitrust liability. Too often, judges have suggested that the absence of a particular plus factor should constitute evidence that no conspiracy exists or ever existed. These plus factors include: concentrated market structure, cartel enforcement mechanisms, stable market shares, intercompetitor communications, and simultaneity of price increases.

This Article performs a three-part analysis for each of these plus factors. First, it describes why the plus factor is probative of collusion and, thus, a plus factor. Second, it illustrates how some courts have distorted the plus factor’s probative value by treating its absence as evidence that no collusion has taken place. Third, using empirical examples and economic theory, it explains why price-fixing conspiracies can exist and thrive even without generating evidence of the particular plus factor that some courts have treated as quasi-elemental.

The plus-factor framework for proving collusion through circumstantial evidence only works if judges properly apply, understand, and interpret plus factors. When courts treat an absence of evidence as evidence of absence, they craft a roadmap for price-fixing cartels to harm consumers while evading antitrust liability. This undermines all the goals of antitrust: compensating victims of price fixing, disgorging ill-gotten gains, and deterring future violations.