Decision theory assumes that agents making choices assign subjective probabilities to outcomes, also at choices where information on probabilities is obviously absent. Yet, Skogh and Wu (2005) show that risk averse agents may gain by risk sharing also at unknown (and unassigned) probabilities of...

Bayesian decision theory assumes that agents making choices assign subjective probabilities to outcomes, even in cases where information on probabilities is obviously absent. Here we show that agents that presume that they are equal risks can share risks mutually beneficially, even if the...

Our “Restated diversification theorem” (Skogh and Wu, 2005) says that risk-averse agents may pool risks efficiently without assignment of subjective probabilities to outcomes, also at genuine uncertainty. It suffices that the agents presume that they face equal risks. Here, the theorem is...