 In formal epistemology, this ends up being very closely related to the question of how an individual ought to update their credences upon learning the credences of others. If a rational group ought to adopt some aggregated belief, then it might also make sense for an individual in the group to adopt the same belief as a result of learning about the credences of his/her peers. In other words, the problems of judgment aggregation, peer disagreement, and testimony are entangled in this literature. (Though see Easwaran et al. (2016) for a discussion of distinctions between these issues.) We’ll focus here on belief aggregation, though we will comment throughout on these other issues.