This article looks first at the process courts use to resolve merger challenges and finds that in the area of product market definition, merger analysis is reasonably strong. Market definition remains complex and subjective, however, and could be improved, or avoided altogether, through econometric techniques such as merger simulation. Judicial analysis of entry is much weaker. Courts ask whether the market is protected by entry barriers but rarely ask whether the barriers are high enough to make entry unprofitable.
The article also examines the results of "marginal" mergers, mergers that would have been blocked had the government and courts been somewhat more aggressive. Measured in this way, merger analysis is not seriously off target: the merger retrospectives find that very few transactions led to sharp price changes. They also find, however, that a large proportion of marginal mergers resulted in small price increases, which suggests that in appropriate cases, enforcement agencies and courts should be more willing to predict anticompetitive effects.
John B. Kirkwood, The Predictive Power of Merger Analysis, 56 ANTITRUST BULL. 543 (2011).