تبلیغات و موتورهای جستجو.مدل رهبری در تبلیغات جستجو

We analyze the role of leadership in a multisided market as search advertising, assuming quantity competition and different entry conditions (with barriers to entry or endogenous entry). The model can be microfounded taking into account network effects, multi-homing on the advertising side and scale in search. If there are barriers to entry and the network effects are strong, there is an incentive for the leader to exploit them and attract more consumers to monopolize advertising. Under barriers to entry, the leading platform has also a strategic incentive to exploit scale in search, to manipulate search results to divert search traffic from other platforms, and to introduce limits to multi-homing, with the aim of expanding its market share and deny scale to competitors.

The theoretical analysis of market leadership is crucial to understanding abuse of dominance issues in imperfectly competitive markets. This paper provides a first theoretical exploration of the role of leaders in multi-sided markets, that is, markets where firms compete by charging multiple sides at the same time, as in the case of the market for search advertising. The economics of multi-sided markets has recently attracted a lot of attention from economists (Rochet and Jean, 2003, Rochet and Jean, 2006, Caillaud and Bruno, 2003, Armstrong, 2006 and Veiga and Weyl, 2012) because it characterizes a number of important markets of the New Economy and generates a number of new intriguing antitrust issues. In particular, a wide interest has been focused on the market for search advertising, whose dominant firm at the global level, Google, is currently being investigated by a number of antitrust authorities. Analyzing this market, it emerges that possible abuses may include preferential treatment for Google's own services in its free (‘universal’) search aimed at drawing off more consumers from vertical search engines, manipulation of the opaque bidding system for sponsored links leading to lower rankings for competing platforms, and contractual restrictions on other platforms and advertisers. However, the theoretical debate on the role of market leaders in multi-sided markets is still limited: most of the literature on multi-sided markets is focused on monopolistic pricing and symmetric price competition between platforms, not on competition for ads between a potentially dominant platform and its followers. In this paper, building on the literature on strategic commitments under different entry conditions (Fudenberg and Tirole, 1985; Etro, 2006) and its recent applications to antitrust and contract theory (Etro, 2010 and Etro, 2011), we advance new insights on modeling leadership in multi-sided markets. As usual, the incentives to adopt different strategies or pre-commitments depend on the entry conditions and on the impact of those strategies or pre-commitments on marginal profitability. We argue that online advertising can be realistically characterized by a fixed number of players in the short-medium run and we examine the impact of different pre-commitments on the equilibrium of this multi-sided market. Our analysis of a Stackelberg duopoly in search advertising suggests that a platform that has reached dominance may have different incentives depending on the strength of the underlying network effects. If the network effects are strong, there is an incentive to exploit them and attract more consumers to monopolize the advertising side, but when they are weak or already exploited there is an incentive to restrict quality and size of services to consumers to reduce the marginal cost per click: this may penalize competition. The results extend to the case of Stackelberg leadership with endogenous entry, but in this case the strategy of the leader does not affect the strategies of the followers and their prices for the ads.

We have analyzed the role of leadership in multi-sided markets, with a particular emphasis on online advertising, which is characterized by a single dominant firm. Our analysis of a Stackelberg duopoly in search advertising suggests that a platform that has reached dominance may have different incentives depending on the strength of the underlying network effects. If the network effects are strong, there is an incentive to exploit them and attract more consumers to monopolize the advertising side, but when they are weak or already exploited there is an incentive to restrict quality and size of services to consumers to reduce the marginal cost per click. The results extend to the case of Stackelberg leadership with endogenous entry, but in this case the strategy of the leader does not affect those of the followers and their prices for the ads. Finally, we have shown that the dominant platform may have incentives to overinvest to build ‘scale in search’ (which is a source of barriers to entry in itself), to manipulate search results to divert search traffic from other platforms, and to introduce contractual or indirect limits to multi-homing by the advertisers. We have developed the simplest model that allows one to examine search advertising while taking in consideration what we believe to be its main aspects, such as quantity leadership, scale in search and multi-homing on the advertising side. Clearly, the model could be developed in many dimensions. One may investigate further the microfoundation on the consumer side, introduce utility from the market transactions online (and therefore network effects from the number of ads to the number of consumers), endogenize the reservation utility as deriving from alternative platforms and analyze the consequences of the equilibria for consumer surplus. On the advertising side, it would be important to introduce competition between multiple advertisers, not only for the ads, but also for the online sales made possible (through search advertising), and analyze again the consequences of the equilibria for consumer surplus. Additional research on the implications of asymmetric models of competition in multi-sided markets appears fruitful to better understand the structure of these markets and the appropriate antitrust policies. This may finally provide new and solid results on what could be the remedies to possible abuses, a topic on which little research is still present. The preliminary impression from our investigation of equilibria with and without free entry is that any intervention aimed at promoting endogenous entry in the market would refrain the leading platform from adopting strategies that may hurt competition and consumers.