This paper is about (non) participation in efficient risk sharing among agents who have ambiguous beliefs about uncertain states of nature. The question we ask is whether and how can ambiguous beliefs give rise to some agents not participating in efficient risk sharing. Ambiguity of beliefs is described by the multiple-prior expected utility of Gilboa and Schmeidler (J Math Econ 18:141–153, 1989), or the variational preferences of Maccheroni et al. (Econometrica 74(6):1447–1498, 2006). The main result says that if the aggregate risk is relatively small, then the agents whose beliefs are the most ambiguous do not participate in risk sharing. The higher the ambiguity of those agents’ beliefs, the more likely is their non-participation. Another factor making non-participation more likely is low risk aversion of agents whose beliefs are less ambiguous. We discuss implications of our results on agents’ participation in trade in equilibrium in assets markets.

本文是关于（不）参与对不确定的自然状态存有歧义的代理商之间的有效风险分担。我们要问的问题是，歧义信念是否以及如何导致某些不参与有效风险分担的主体。Gilboa和Schmeidler（J Math Econ 18：141–153，1989）或Maccheroni等人的变异偏好描述了信念的歧义。（Econometrica 74（6）：1447-1498，2006）。主要结果表明，如果总风险相对较小，则信念最模糊的主体不会参与风险分担。这些代理人的信念的歧义性越高，他们不参与的可能性就越大。导致不参与的可能性更大的另一个因素是信念不太模糊的代理商的低风险厌恶情绪。