Opinion Aggregation and Individual Expertise

Group judgments are often influenced by their members’ individual expertise. It is less clear, though, how individual expertise should affect the group judgments. This paper surveys a wide range of formal models of opinion aggregation and group judgment: models where all group members have the same impact on the group judgment, models that take into account differences in individual accuracy, and models where group members revise their beliefs as a function of their mutual respect. The scope of these models covers the aggregation of propositional attitudes, probability functions, and numerical estimates. By comparing these different kinds of models and contrasting them with findings in psychology, management science and the expert judgment literature, we gain a better understanding of the role of expertise in group agency, both from a theoretical and an empirical perspective.