1. IntroductionThis paper reexamines the phenomenon of free riding in entry deterrence when established firms in an oligopoly are unable to coordinate their entry preventing activities. Previous authors (e.g., Bernheim 1984; Gilbert and Vives 1986; Waldman 1987, 1991; Appelbaum and Weber 1992) have highlighted the public good aspect of noncooperative entry prevention--if costly entry deterring actions are successfully undertaken by a proper subset of the incumbents, then incumbents outside of that subset cannot be excluded from the benefits of deterred entry. It is in this sense that entry deterrence acquires the nature of a public good. This observation has prompted previous researchers to raise the "free rider" question (with its associated welfare implications): Can there occur underinvestment in entry deterrence due to the incentive for each firm to free ride on the others' (costly) entry preventing activities?The free rider problem in entry deterrence is first mentioned in the sequential entry model of Bernheim (1984). However, though Bernheim discusses the possibility of free riding in his model, the free rider problem is not the main focus of his paper. In fact, as pointed out by Waldman (1987, p. 309, footnote 2), the author's discussion of the role of the free rider problem is "... somewhat vague as regards whether Bernheim feels the free rider problem would ever be important in a noncooperative entry deterrence setting."1Gilbert and Vives (1986) is the first paper in which the underinvestment issue is explicitly addressed. The authors define underinvestment in entry deterrence to be associated with one or more of the following:"(a) Incumbents' total profits are higher preventing than allowing entry, but the (unique) industry equilibrium allows entry.(b) Either entry prevention or entry may be an industry equilibrium, but incumbents' profits are higher when entry is prevented.(c) An established monopoly (or colluding incumbents) prevents entry in more situations than an established, noncooperating oligopoly." (p. 77) Label (a), (b), and (c) as underinvestment of type 1, 2, and 3, respectively. Gilbert and Vives (G&V) go on to show that in none of these respects is there underinvestment in their quantity setting homogeneous product model. On the contrary, they demonstrate a strong possibility of overinvestment.G&V consider a situation where symmetric noncooperative incumbents with constant marginal costs of production make credible commitments to outputs in the preentry stage.2 The entrant incurs a fixed entry cost if it enters the industry and makes its entry and output decision after observing the incumbents' output choices. Consequently, there exists a "limit output," which if jointly produced by the oligopoly, deters entry.3 G&V find that entry is prevented when limit outputs are small, while entry is allowed for larger limit outputs. For limit outputs in an intermediate range, both allowing entry and preventing entry are equilibria. They prove that in this intermediate range where both entry accommodating and entry preventing equilibria coexist, the unique entry equilibrium Pareto dominates every deterrence equilibrium. In other words, compared with any deterrence equilibrium (there is typically a continuum of such equilibria) the accommodation equilibrium yields strictly higher profits to every incumbent. Hence, if the industry settles on an entry preventing equilibrium, the implication is that overinvestment exists because, by jointly reducing incumbents' outputs and allowing entry, every incumbent can be made better off.This paper introduces product differentiation into the G&V model and shows that sufficiently large amounts of product differentiation can generate underinvestment in entry prevention. The intuition is straightforward. Consider an incumbent's profit in any entry deterring equilibrium where exactly the limit output is produced by the oligopoly. …
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