The patterns and mechanisms of collective decision making in humans and animals have attracted both empirical and theoretical attention. Of particular interest has been the variety of social feedback rules and the extent to which these behavioral rules can be explained and predicted from theories of rational estimation and decision making. However, models that aim to model the full range of social information use have incorporated ad hoc departures from rational decision-making theory to explain the apparent stochasticity and variability of behavior. In this paper I develop a model of social information use and collective decision making by fully rational agents that reveals how a wide range of apparently stochastic social decision rules emerge from fundamental information asymmetries both between individuals and between the decision makers and the observer of those decisions.
As well as showing that rational decision making is consistent with empirical observations of collective behavior, this model makes several testable predictions about how individuals make decisions in groups and offers a valuable perspective on how we view sources of variability in animal, and human, behavior.agent-based model | collective behavior | rational choice | social information | utility C ollective decision making is a ubiquitous task for social animal species, including humans (1). Whether deciding where to forage, which nest site to choose, or when to move, individual decisions are greatly informed by observing the choices that others make. As recently as 2008, Ward et al. (ref. 2, p. 1) were able to state that "little is known about the mechanisms underlying decision-making in vertebrate animal groups." Since then, however, a large literature has explored the rules governing social information use in collective decisions across various taxa, for example in insects (3), fish (2, 4), birds (5, 6), and mammals (7, 8), including primates (9) and humans (10, 11). What links decision making in all of these groups is the presence of social reinforcement, with individuals demonstrating a strong preference for an option chosen by others, which increases with the number of others who have selected it. This reinforcement can be expressed as a social response function-the probability of selecting a given option conditioned on the number of other individuals that have previously chosen it. A large degree of variation has been observed in these social response functions, ranging from linear relationships (e.g., refs. 3 and 12) to strongly nonlinear "quorum" rules (13), where the apparent attractiveness of an option appears to increase exponentially with the number of individuals choosing it, before saturating as this number passes a quorum level. In addition to variation between taxa, studies have also highlighted how the same species can exhibit different patterns of collective behavior under different laboratory or field conditions (14-17), highlighting the potential importance of context-dependent social responses.Complementing these em...