In this study we analyse the role of speculation in forging cross-market linkages between agriculture, equity and crude oil over the period 1992-2014. The market interdependence of ten U.S. traded agricultural commodities futures is measured through the spillover index of Diebold and Yilmaz (2009, 2012) and the dynamic conditional correlation framework of Engle (2002). Utilising data from the U.S. Commodity Futures Trading Commission, ve dierent measures of speculation are constructed, which are used to examine the long-run and short-run dynamics between market integration and speculation. To explore time-varying characteristics in this relationship, and as a test for robustness, we perform a sub-sampling analysis for the periods 1992-2006 and 2006-2014. We show that cross-market linkages grew stronger post-2005, particularly in the aftermath of the 2008 global financial crisis. The results of our econometric analysis indicate that any conclusions regarding the role of speculation in this process are highly sensitive both to the choice of market integration measure, as well as to how the extent of speculation is captured. Overall, though, there is little to indicate that speculation has played an important role in creating cross-market linkages. We do provide some evidence of market integration increasing with market size, but other factors, such as inflation and exchange rates, seem to provide better explanations of agriculture-equity-energy price dynamics. In line with previous research, we also find market interdependence to increase with stock market uncertainty, which suggests that the diversification benefits of commodity futures investments are actually reduced when needed the most. Considered together with our findings on the sizes of markets, which are increasingly made up of speculators, it appears at least possible that financialisation has made food markets more vulnerable to disturbances in financial markets.

La thèse est composée de trois parties. La première présente un certain nombre de mesures de dépendance extrême. Une application sur les actions et les obligations de 49 pays montre que la théorie des valeurs extrêmes multivariées conduit aux résultats différents de ceux issus du coefficient de corrélation, mais relativement proches de ceux obtenus du rho de Spearman conditionnel multivarié. Cette partie évalue aussi le risque de pertes importantes simultanées. La deuxième partie examine les déterminants des co-mouvements extrêmes entre 5 pays core et 49 pays non core. Les mécanismes de transmission des chocs varient de la période moins récente à la période récente, des pays développés aux pays émergents, des chocs normaux aux chocs extrêmes. La troisième partie étudie le rôle de valeur refuge de l’or sur la période 1986-2012. Les gains positifs extrêmes de l'or peuvent être liés aux pertes extrêmes du S&P. Cependant, ce lien n'est pas toujours valable, il évolue dans le temps et serait conditionné par d'autres facteurs. / The thesis consists of three parts. The first part introduces a number of measures of extreme dependency. An application on stock and bond markets of 49 countries shows the multivariate extreme value theory leads to results which are different from those from the correlation coefficient, but relatively close to those obtained from multivariate conditional Spearman's rho. This part also assesses the risk of simultaneous losses. The second part examines the determinants of extreme co-movements between 5 core countries and 49 non-core countries. Transmission mechanisms of shocks vary from less recent to recent period, from developed to emerging markets, from normal to extreme shocks. The third part examines the role of safe haven of gold over the period 1986-2012. Extreme positive gains of gold can be linked to extreme losses of S&P. However, this relationship is not always valid, it evolves over time and could be determined by other factors.