Models of spatial competition are typically static, and exhibit multiple free-entry equilibria. Incumbent firms can earn rents in equilibrium because any potential entrant expects a significantly lower market share (since it must fit into a niche between incumbent firms) along with fiercer price competition. Previous research has usually concentrated on the zero-profit equilibrium, at which there is normally excessive entry, and so an entry tax would improve the allocation of resources. At the other extreme, the equilibrium with the greatest rent per firm normally entails insufficient entry, so an entry subsidy should be prescribed. A model of sequential firm entry (with an exogenous order of moves) resolves the multiplicity problem but raises a new difficulty: firms that enter earlier can expect higher spatial rents, and so firms prefer to be earlier in the entry order. This tension disappears when firms can compete for entry positions. We therefore suppose that firms can commit capital early to the market in order to lay claim to a particular location. This temporal competition dissipates spatial rents in equilibrium and justifies the sequential move structure. However, the policy implications are quite different once time is introduced. An atemporal analysis of the sequential entry process would prescribe an entry subsidy, but once proper account is taken of the entry dynamics, a tax may be preferable.

We propose a methodology for estimating the competition effects from entry when firms sell differentiated products. We first derive precise conditions under which Bresnahan and Reiss' entry threshold ratios (ETRs) can be used to test for the presence and to measure the magnitude of competition effects. We then show how to augment the traditional entry model with a revenue equation. This revenue equation serves to adjust the ETRs by the extent of market expansion from entry, and leads to unbiased estimates of the competition effects from entry. We apply our approach to seven different local service sectors. We find that entry typically leads to significant market expansion, implying that traditional ETRs may substantially underestimate the competition effects from entry. In most sectors, the second entrant reduces markups by at least 30%, whereas the third or subsequent entrants have smaller or insignificant effects. In one sector, we find that even the second entrant does not reduce markups, consistent with a recent decision by the competition authority.

These contributions discuss a number of important developments over the past decade in a newly established and important field of economics that have led to notable changes in views on governmental competition policies. They focus on the nature and role of competition and other determinants of market structures, such as numbers of firms and barriers to entry; other factors which determine the effective degree of competition in the market; the influence of major firms (especially when these pursue objectives other than profit maximization); and decentralization and coordination under control relationships other than markets and hierarchies.ContributorsJoseph E. Stiglitz, G. C. Archibald, B. C. Eaton, R. G. Lipsey, David Enaoua, Paul Geroski, Alexis Jacquemin, Richard J. Gilbert, Reinhard Selten, Oliver E. Williamson, Jerry R. Green, G. Frank Mathewson, R. A. Winter, C. d'Aspremont, J. Jaskold Gabszewicz, Steven Salop, Branko Horvat, Z. Roman, W. J. Baumol, J. C. Panzar, R. D. Willig, Richard Schmalensee, Richard Nelson, Michael Scence, and Partha Dasgupta