Individual Confidence-Weighting and Group Decision-Making

Abstract

Group-living species frequently pool individual information so as to reach consensus decisions such as when and where to move, or whether a predator is present. Such opinion-pooling has been demonstrated empirically, and theoretical models have been proposed to explain why group decisions are more reliable than individual decisions. Behavioural ecology theory frequently assumes that all individuals have equal decision-making abilities, but decision theory relaxes this assumption and has been tested in human groups. We summarise relevant theory and argue for its applicability to collective animal decisions. We consider selective pressure on confidence-weighting in groups of related and unrelated individuals. We also consider which species and behaviours may provide evidence of confidence-weighting, paying particular attention to the sophisticated vocal communication of cooperative breeders. Theory as applied to collective decision-making by non-human animals frequently assumes that all animals have equal decision-making abilities and access to equal-quality information. Decision theory shows that the optimal group decision-making strategy is to weight contributions to group decisions according to the decision accuracy or ‘subjective confidence’ of the contributor. Human groups have been shown to be able to combine judgements optimally, accounting for variations in subjective confidence. Collectively deciding animals, particularly groups of cooperative breeders, have sophisticated vocal communication abilities and may provide suitable systems to test theory. The time taken to reach a decision, or hesitancy, provides a link between optimal individual decision-making and optimal group decision-making, and may easily be evaluated by individuals.