Reservation of Judgment and Robust Collective Decisions

TL;DR

This paper explores preference aggregation under ambiguity, introducing a dual Pareto principle that often results in dictatorship, and proposes weakened rules to avoid spurious unanimity, ensuring all plausible priors are considered.

Contribution

It introduces a dual Pareto principle for preference aggregation under ambiguity and characterizes new belief-aggregation rules that prevent discarding plausible priors.

Findings

Dual Pareto principle often leads to dictatorship in taste aggregation.

Weakening the principle avoids spurious unanimity.

New belief-aggregation rules preserve all plausible priors.

Abstract

This paper studies preference aggregation under ambiguity when agents have incomplete preference relations due to imprecise beliefs. We introduce the "dual" of the Pareto principle, which respects unanimity among individuals, including those with unexpressed opinions. Our first theorem shows that, in most cases, this principle leads to a dictatorial rule in taste aggregation. We argue that this stems from the problem of spurious unanimity, even when the individuals have the same prior set. By weakening the above principle to avoid respecting spurious unanimity, the second theorem characterizes novel belief-aggregation rules, under which society does not discard any combination of plausible priors.