Sequential aggregation of judgments

Bezalel Peleg
Shmuel Zamir

We consider a standard model of judgment aggregation as presented, for example, in Dietrich (2015). For this model we introduce a sequential aggregation procedure (SAP) which uses the majority rule as much as possible. The ordering of the issues is assumed to be exogenous. The exact definition of SAP is given in Section 3. In Section 4 we construct an intuitive relevance relation for our model, closely related to conditional entailment. Unlike Dietrich (2015), where the relevance relation is given exogenously as part of the model, we require that the relevance relation be derived from the agenda. We prove that SAP has the property of independence of irrelevant issues (III) with respect to (the transitive closure of) our relevance relation. As III is weaker than the property of proposition-wise independence (PI) we do not run into impossibility results as does List (2004) who incorporates PI in some parts of his analysis. We proceed to characterize SAP by anonymity, restricted monotonicity, local neutrality, restricted agenda property, and independence of past deliberations (see Section 5 for the precise details). Also, we use this occasion to show that Roberts’s (1991) characterization of choice by plurality voting can be adapted to our model.

May, 2017