VERDIER Marianne

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This article presents an overview of the literature on platform markets. Several recent papers have extended the pioneer works of Rochet and Tirole [2003] or Armstrong [2006] by addressing unexplored issues such as the measure of market power in the presence of crossed-externalities, or the impact of bundling on social welfare. These new results can help policy makers to achieve a better understanding of these markets. Classification JEL : E42, G21, L96.

Consumers have bounded rationality and are subject to various cognitive biases. The thesis studies the consequences of rationality biases on consumer behavior and the implications for consumer policy. Each of the three chapters of the thesis is devoted to a particular bias (quality overestimation, utility anticipation errors, projection bias) in a given competitive context. The first two chapters are built on standard duopoly models to which rationality biases are incorporated: the first is a duopoly with horizontal differentiation inspired by Dixit (1979), while the second considers a vertical differentiation model adapted from Gabszewicz & Thisse (1979). The third chapter extends to three periods the projection bias model proposed by Loewenstein et al. (2003). I conclude that, while cognitive biases may lead to suboptimal choices in some cases (Chapters 1 and 2), naive consumers may also have an advantage over sophisticated agents (Chapter 3). This finding argues for a detailed and measured intervention in the market. Finally, policy recommendations are formulated: I advocate a renewed approach to consumer law, which would no longer be based primarily on consumer information but more on cognitive remedies. Examples of concrete measures are discussed throughout the thesis.

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In this paper, we analyze the impact of cooperation on R&D investments in a two-sided market, where platforms compete in quantities. We show that if indirect externalities are of a moderate magnitude, the threshold degree of spillovers above which cooperation spurs R&D investments and enhances social welfare increases with the degree of externalities. If indirect externalities are of a strong magnitude, cooperation can also be beneficial in terms of welfare for low degrees of spillovers.

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In this paper, we discuss how fraud losses impact the price structure chosen by a monopolistic payment platform, if merchants can invest in fraud detection technologies. We show that liability rules bias the structure of the prices charged by the platform to consumers and merchants with respect to a case in which such a responsibility regime is not implemented. If consumers are liable for fraud, the profit-maximizing price structure is neither biased in favor of consumers nor merchants. If consumers are not liable for fraud, the platform lowers the price for merchants to provide them with investment incentives. Under the zero liability rule for consumers, the profit-maximizing allocation of fraud losses maximizes social welfare.

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The ownership and use of payment instruments have grown considerably in industrialized countries. The success of payment cards can be explained by the presence of interbank payment systems, such as "Visa" or "MasterCard", which organize the interactions between the cardholder's bank, the issuer, and the merchant's bank, the acquirer. This thesis focuses on a particular cost allocation mechanism practiced by payment platforms: interchanges. Interchange is the subsidy paid by the merchant's bank to the cardholder's bank each time a consumer uses his payment card. By lowering the price paid by the consumer for a transaction, the interchanges contribute to encouraging the use of payment cards at the expense of cash. The thesis is structured around two issues. The first problem concerns the effect of interchanges on the investments of card payment system actors. The second problematic deals with the impact of interchanges on the substitution between payment cards and cash. In the first chapter of the thesis, we conduct an empirical analysis of the payment card industry in France and in Europe. In the second chapter of the thesis, we build a theoretical model to present the results of the interchanges literature. In the third chapter, we address the question of the influence of interchanges on banks' investments to improve the quality of the payment service, and on merchants' investments to bypass the platform by issuing proprietary cards. In the fourth chapter of the thesis, we discuss the impact of interchanges on the substitution mechanisms between card and cash.

The ownership and use of payment instruments have grown considerably in industrialized countries. The success of payment cards can be explained by the presence of interbank "payment systems", which organize the interactions between the cardholder's bank, the issuer, and the merchant's bank, the acquirer. This thesis focuses on a particular cost allocation mechanism used by payment platforms: interchanges. The thesis addresses two issues. The first problem concerns the effect of interchanges on the investments of card payment system actors. The second problematic deals with the impact of interchanges on the substitution between payment cards and cash. In the first chapter of the thesis, we conduct an empirical analysis of the payment card industry in France and in Europe. In the second chapter, we build a theoretical model to present the results of the interchanges literature. In the third chapter, we address the question of the influence of interchanges on banks' investments to improve the quality of the payment service, and on merchants' investments to bypass the platform by issuing proprietary cards. In the fourth chapter of the thesis, we discuss the impact of interchanges on the substitution mechanisms between card and cash.