 Other scholars, including Coase himself, have disputed this account. These critics argue that vertical contractual restraints were more than sufficient to protect GM's interests and point out that at the time that Fisher Body supposedly acted opportunistically, GM already owned sixty percent of Fisher Body's common stock (Coase 1988, 2000; Casadesus-Masanell and Spulber 2000; Freeland 2000). Klein, in turn, responded by arguing that the relevant quasi-rents resulted from firm-specific human (rather than physical) capital and by placing greater emphasis on Fisher Body's supposed refusal to locate its plants near GM's (Klein 1988, 2000). Networks in Telecommunications sufficient to offset any concomitant anticompetitive effects. Whether a particular instance of vertical integration impedes or promotes competition depends on which of these two effects dominates. 33 Determining whether a particular form of vertical integration will enhance or reduce economic welfare is thus an empirical question that turns on the particular market structure and the nature of the available efficiencies. Although some have questioned whether the empirical literature is sufficiently developed to support any clear policy inferences,34 recent surveys of the empirical literature on vertical integration and vertical restraints found that the existing studies overwhelmingly support for the proposition that vertical integration and vertical restraints tend to promote, rather than harm, competition. 35 All of the rationales discussed up to this point focus on how best to allocate the network that already exists, by organizing production SO that it consumes the fewest resources and by allocating outputs to those consumers who can put them to the best use. In focusing on allocating the network that already exists today, these rationales overlook the equally (if not more) important question of how to create incentives to invest in new network technologies that will compose the optimal network of tomorrow. In other words, the current policy debat