Bayesian interactions and collective dynamics of opinion: Herd behavior and mimetic contagion

Much recent work has been devoted to the analysis of herd behavior within sequential decision models. The present article generalizes their results to non-sequential contexts. We will show that, as soon as the hypothesis of sequentiality is dropped, a large variety of situations can be observed. Our model has been designed to study the collective learning process through which a group of interacting agents deals with environmental uncertainty. The crucial question revolves around the relative weight given by each individual to the different sources of information: his private information and his observation of the group opinion.