Agricultural price instability and optimal stabilisation policies.

Summary In French: Cette thèse propose une analyse des politiques de stabilisation des prix alimentaires dans les pays pauvres. In order to represent the situation in these countries, we consider in a rational expectations storage model that consumers cannot insure themselves against price risk and that they are risk averse. The market incompleteness justifies public intervention and optimal stabilization policies are analyzed. An optimal public storage policy involves an increase in the level of storage. This additional storage leads to the crowding out of all private storers by eliminating speculative profit opportunities. Since the use of complex public intervention rules is unlikely in poor countries, we compare optimal food storage policies to simple rules such as a subsidy to private storage or a price band defended by public storage. Government involvement leads to welfare gains relative to a discretionary policy due to the possibility of manipulating producers' expectations and thus inducing them to stabilize prices. Simple stabilization rules allow for gains close to those obtained with optimal policies. In an open economy, the stabilization instruments are trade policy and storage. A storage policy unaccompanied by a trade policy does not benefit consumers, because the benefits of stabilization dissipate on the world market. On the contrary, an optimal trade policy increases stabilization by exploiting the world market.