Network Externalities, Mutuality, and Compatibility

Positive network externalities can arise when consumers benefit from the consumption of compatible products by other consumers (user-positive consumption externalities) or, alternatively, when they incur costs from the consumption of incompatible products by other consumers (nonuser-negative consumption externalities). But whereas user-positive externalities are typically mutually imposed and imply mutual benefit because they relate to interoperability, with nonuser-negative externalities the costs of incompatibility may be imposed unilaterally and borne asymmetrically. For example, increased risks of death and injury on the roads due to the co-existence of large and small vehicles are imposed exclusively by the owners of the large vehicles and borne exclusively by the occupants of the small vehicles. This paper compares the social optimality of incentives for compatibility under regimes involving user-positive and nonuser-negative externalities. Earlier work with respect to user-positive externalities (e.g., Katz and Shapiro, 1985) suggests that firms with relatively small networks or weak reputations tend to be biased in favor of compatibility, while individual firms' incentives for compatibility are suboptimal when their networks are closely matched in size. Meanwhile, intuition suggests that with nonuser-negative externalities incentives for incompatibility should always be excessive, reflecting the notion that activities involving unilaterally imposed negative externalities will always be overprovided by the market (in the absence of regulation or Coaseian mitigation). Using a "location" model of differentiated products, we find that, under both regimes, incentives for compatibility tend to be suboptimal when firms' networks are close in size, and excessive for the small firm when the networks differ greatly in size. Surprising public policy implications with respect to externalities are discussed