Torrin Liddell (Indiana University)
Abstract. For a group to have common knowledge of some fact, they must all know the fact, but also they must all know that they all know it, and this knowledge must also be known, and so on. Common knowledge of behavioral rules and intentions is crucial to basic social tasks, ranging from cooperative hunting to oligopoly collusion to riots, revolutions, and the evolution of social norms and human culture. Yet little is known about how the need for common knowledge leaves a trace on the dynamics of a social network. We find that the need for common knowledge can yield great inequalities in success, in contrast to the relative equality that results when practices spread by contagion alone. Moreover, we show how basic properties of an individual's position in a network — primarily clustering — provide strong signals of an individual's ability to successfully participate in common knowledge tasks. These signals are distinct from those expected when practices are contagious, or when people rely on less-sophisticated heuristics that do not lead to true common knowledge. Thus, the distribution of success as well as simple network analysis can provide robust knowledge of the underlying cognitive processes that drive group decision-making in a given task.