The role of networks in antitrust investigations

Antitrust investigations typically focus on the competitive pressures coming from within the defined markets of interest. However, competitive pressures can also come from other markets. Even when individually these markets place only weak constraints on one another, collectively they may matter. A networks approach to modelling competition permits a systemic view of competition that can sometimes paint a more accurate picture. We demonstrate this through some simple examples, and show more generally how tools from the networks literature can be applied to capture competition across a system of interrelated markets. As a leading example, we consider antitrust investigations into supermarkets where local geographic markets have been used as the basis of investigation.