In this thesis, we study if credit rating agencies (CRAs) are capable, through their rating process, of discover information that it is valued by the market. Additionally, we investigate if CRAs are able to propagate their findings to the market. if Specifically, we study the differences between issuer-paid and investor-paid credit rating agencies, and how those differences shape the characteristics of their credit ratings and ultimately, if investors can profit from credit rating announcements. For our research we use a large dataset of rating announcements from 1997 to 2012, which includes information of four credit rating agencies (CRAs), Egan-Jones Ratings Company (EJR), Fitch, Moody's and Standard and Poor's, which representing investor-paid and issuer-paid CRAs. This allows us to compare these two kind of agencies and its ratings. In the first essay we study what variables explain the rating coverage of an investor-paid credit rating agency. We show that probability of being covered by EJR is positively related with the size of the firm, the level of institutional ownership of the firm, stock analysts and issuer-paid CRAs level of coverage, while it is negatively related to the firm's corporate governance. We found that the likelihood of being covered by EJR augments after regulatory changes and most interestingly, since EJR received the NRSRO certification. In the second essay we compare the timeliness of rating changes produced by EJR and the issuer-paid CRAs representatives. We found that the lead effect of investor-paid over issuer-paid CRAs has weakened in recent years, while Granger causality is bidirectional and therefore a lead-lag relationship cannot be established. Finally, stock prices manifest statistically significant abnormal reactions to downgrades of all agencies; however, abnormal negative returns are significantly higher for EJR. Our results support the hypothesis that issuer-paid agencies improve the quality and timeliness of their ratings when they see their market power threatened by tighter regulations. Nevertheless, event studies illustrate that markets still price stocks under the assumption that investor-paid rating actions carry superior information. Finally, our third essay found that purchasing (selling short) stocks with positive (negative) rating announcements generates portfolios with positive annual abnormal returns when investors react immediately to rating announcements. Returns are higher for stronger announcements (i.e. rating changes over rating outlooks) and for an investor-paid agency rather than an issuer-paid agency. When we introduced transaction costs, only the investor-paid agencies' announcements lead to positive abnormal returns. Additionally, when we included a delay in the reaction of investors to rating announcements, all positive abnormal returns net of transaction costs disappeared. Finally, our results suggests that the differences between investor-paid and issuer-paid agencies are based on their dissimilar business models rather than their regulatory status.

Sur les marchés agricoles, les producteurs encourent les risques de prix et de production ainsi que d'autres types de risques liés aux aléas de production. Ces risques impactent l'activité du producteur et pourraient diminuer ses revenus. La mondialisation des marchés, en particulier ceux des matières premières agricoles, permet de développer une stratégie de couverture en utilisant des instruments comme les contrats à terme. Cependant, la situation selon laquelle une position basée seulement sur un contrat futures devrait couvrir tous les risques, entraîne un marché incomplet. Le producteur en recherche de meilleure stratégie de couverture pour ajouter un contrat d'assurance ou d'option pour garantir davantage ses revenus, surtout lorsque les rendements des cultures prévus diminuent. Nous étudions, ici les stratégies de couverture dans le cadre statique, ainsi que dans le cadre de temps continu. Avant, nous analysons le comportement des prix des matières premières agricoles en utilisant diverses approches statistiques afin de suggérer la modélisation des prix adéquate aux données. La stratégie de couverture statique comprend également le processus de retournement de positions qui pourrait entraîner d'autres risques supplémentaires en raison de l'écart entre les nouveaux contrats à terme et des contrats à terme à proximité ainsi que la couverture inter-culture. Nous proposons une stratégie de couverture qui combine des contrats futures et d'assurance. Comme la prise de décisions dans le cadre statique ne tient pas compte des mouvements quotidiens de prix le long de l'horizon de couverture, la stratégie de couverture optimale en temps continu combine des positions en contrat à terme et options tout en prenant en compte les sauts et la saisonnalité dans la dynamique des prix. / In agricultural markets, producers incur price and production risks as well as other risks related to production contingencies. These risks impact the producer activity and could decrease his income. The globalization of markets, particularly those of agricultural commodities, provides hedging instruments including futures contracts which will serve to develop a hedging strategy. However, the situation whereby a single futures contract-based positions could offset many risks leads to incomplete market. Especially, an producer looking for better hedging strategy could also include insurance, option contract or mutual funds to further guarantee his income, specially when crop yields are lower than expected.vspace{0.25cm}We investigate the hedging strategies in static framework as well as in continuous time framework. Prior, we analyze the behavior of agricultural prices using various statistical approaches and suggest appropriate price modeling for data at hands. The static hedging strategy also accounts for rollover process which gives raise to additional risks due to spread between new futures and nearby futures and inter-crop hedging. We particularly address hedging strategy that combines futures and insurance contracts. Since decisions making in static framework does not include price changes along the hedging horizon, optimal hedging strategy in continuous time framework will take into account jumps and seasonality by combining futures and option contracts.

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