The ex ante aggregation of opinions under uncertainty

Abstract

This paper presents an analysis of the problem of aggregating preference order- ings under subjective uncertainty. Individual preferences, or opinions, agree on the ranking of risky prospects, but are quite general becausewe do not specify the perception of ambiguity or the attitude toward it. A convexity axiom for the ex ante preference characterizes a (collective) decision rule that can be interpreted as a compromise between the utilitarian and the Rawlsian criteria. The former is characterized by the independence axiom as in Harsanyi (1955). Existing re- sults are special cases of our representation theorems, which also allow us to in- terpret Segal’s (1987) two-stage approach to ambiguity as the ex ante aggregation of (Bayesian) future selves’ opinions.