Network structures of a centralized and a decentralized market. A direct comparison.

Résumé En

A fundamental assumption in economics is that rational individuals act in their ownself interest. One implication is that, when trading, buyers are supposed to seek for thelowest price and sellers for the highest one and social interactions are not considered.It is now largely accepted that social relationships affect the efficiency of a marketstructure (centralized or decentralized) .The objectives of the current study is to examine the network structures of a veryspecific market : the Boulogne-sur-mer fish market. On this market two market design (auctions and bilateral exchanges) coexist, each beeing used by the same buyers and sellers, exchanging similargoods. For each sub-market we examine (1) the global networkstructure, (2) the local network structure, and (3) we identify the traders characteristicsthat best explain the network structures. The objective is to identify thethe influence of trust nad the influence of reputation in the individual choicesof trading partners.Structural measures are used to characterize networks structures. Exponential random graph models are used to evaluate how trader characteristics explain purchasingpatterns, and how the influence of these characteristics vary with the market mechanism.We bring into the light that, when the transaction links on the auction market reflects the economic constraints of the partners, the relationships on the bilateral marketdepends on something more. Clearly, the prices of the bilateral transactions are the consequences of economics and non economics determinants. At first glance, the stableco-existence of two market structures looks like a paradox. Our results help to understand the distinctive characteristics and functioning of each sub-market. This discussioncontributes to the debate about the efficiency of market structures.