This dissertation consists of two essays. The first essay develops a new methodology for estimating the probability of informed trading from the observed quotes and depths, by extending the Copeland and Galai (1983) model. This measure (PROBINF) can be computed for each quote and it represents the specialist's ex-ante estimate of the probability of informed trading. I show that PROBINF exhibits a strong and robust relationship with the observed level of insider trading and with measures of the price impact of trades (ë) estimated based on the models of Glosten and Harris (1988), Madhavan and Smidt (1991) and Foster and Viswanathan (1993). In contrast, the alternative measure of the probability of informed trading (PIN) developed by Easley, Kiefer, O'Hara and Paperman (1996) exhibits a weaker and less robust relationship with insider trading and price impact of trades. The time series pattern of PROBINF in an intra-day analysis around earnings announcement is consistent with previous findings regarding informed trading. An important advantage of PROBINF over PIN and other measures of information asymmetry such as price impact of trades and adverse selection component of the spread is that, unlike these measures, it can be estimated for each quote, and thus can also be used to measure intra-day changes in informed trading and information asymmetry. In the second essay, I examine whether the underwriting syndicate composition influences the secondary market liquidity for initial public offerings (IPOs). Specifically, I argue that co-managers improve the liquidity of IPOs through the other services they provide, besides market making. Using a comprehensive sample of initial public offerings completed between January 1993 and December 2005, I find that IPOs with a high number of co-managers in their syndicates have lower spreads and a lower level of information asymmetry in the aftermarket. I argue that the information produced during the premarket and the analyst coverage in the aftermarket are the main channels through which co-managers mitigate the information asymmetry risk in the secondary market. / Ph. D.

L’introduction en Bourse est une opération de financement majeure dans la vie d’une entreprise. Le choix des intermédiaires-conseils revêt une importance capitale, particulièrement celui du syndicat bancaire dont les responsabilités sont importantes, à l’image de la certification du prix d’émission et la réussite du placement des titres. Les multiples asymétries d’information et les anomalies des marchés boursiers impliquent pour l’émetteur de prendre les bonnes décisions. Nous nous intéressons particulièrement à la compréhension des critères de sélection utilisés par l’entrepriseémettrice dans le choix de la banque chef de file. Parmi ceux-ci, le critère de réputation dont les travaux empiriques, majoritairement outre-Atlantique, ont mis en évidence l’impact positif dans l’atténuation des déviations observées sur le marché boursier. La démarche suivie pour argumenter cette thèse nous a conduits, dans le premier chapitre à justifier notre positionnement théorique et à développer notre cadre de recherche. Dans le deuxième chapitre, nous présentons une étude de cas de l’introduction en Bourse d’Electricité de France, opération européenne majeure réalisée durant cette dernière décennie et entreprenons une démarche qualitative dans laquelle nous prenons en compte la réalité économique et financière. Enfin, la vérification empirique de cette problématique est développée dans le troisième chapitre. Nous réalisons une étude statistique sur un échantillon d’introductions en Bourse européennes afin d’apporter des éclaircissements sur la structure de la syndication bancaire et examinons le lien de cette structure avec la réputation de la banque chef defile. / The initial public offering is a major financing operation in a company’s life. The choice of advising intermediaries is of paramount significance. This is the case in particular for the underwriting syndicate whose responsibilities, such as the certification of the issue price and the successful placement of securities are important. Multiple information asymmetries and anomalies in stock markets involve the issuer making the right decisions. We pay particular attention to a thorough understanding of the selection criteria used by the issuing firm in the choice of the lead manager. One of these is the reputation criteria, observed in empirical studies, mostly from across the Atlantic, which have highlighted its positive impact in mitigating stock market deviations. The approach we followed to develop this thesis led us, in the fist chapter, to justify our theoretical positioning and to develop our research framework. In the second chapter, we carried out a case study of the Electricité De France IPO, a major European issue during this last decade and undertook a qualitative approach in which we covered the economic and financial realities. Finally, the empirical verification of this issue was developed in the third chapter. We carried out a statistical study based on a sample of European IPOs in order to clarify the structure of theunderwriting syndicate and explore the relationship of this structure with the lead manager reputation.