Original Paper

Social Choice and Welfare

, Volume 35, Issue 4, pp 595-626

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Bayesian group belief

  • Franz DietrichAffiliated withDepartment of Philosophy, Logic and Scientific Method, London School of EconomicsDepartment of Quantitative Economics, Maastricht University Email author 


If a group is modelled as a single Bayesian agent, what should its beliefs be? I propose an axiomatic model that connects group beliefs to beliefs of the group members. The group members may have different information, different prior beliefs and even different domains (algebras) within which they hold beliefs, accounting for differences in awareness and conceptualisation. As is shown, group beliefs can incorporate all information spread across individuals without individuals having to explicitly communicate their information (that may be too complex or personal to describe, or not describable in principle in the language). The group beliefs derived here take a simple multiplicative form if people’s information is independent (and a more complex form if information overlaps arbitrarily). This form contrasts with familiar linear or geometric opinion pooling and the (Pareto) requirement of respecting unanimous beliefs.