The Median Rule in Judgement Aggregation
40 Pages Posted: 10 Feb 2018
Date Written: January 30, 2018
A judgement aggregation rule takes the views of a collection of voters over a set of interconected issues, and yields a logically consistent collective view. The median rule is a judgement aggregation rule that selects the logically consistent view which minimizes the average distance to the views of the voters (where the “distance” between two views is the number of issues on which they disagree). In the special case of preference aggregation, this is called the Kemeny rule. We show that, under appropriate regularity conditions, the median rule is the unique judgement aggregation rule which satisfies three axioms: Ensemble Supermajority Efficiency, Reinforcement, and Continuity. Our analysis covers aggregation problems in which different issues have different weights, and in which the consistency restrictions on input and output judgments may differ.
Keywords: Judgement Aggregation, Majoritarian, Reinforcement, Consistency, Median
JEL Classification: D71
Suggested Citation: Suggested Citation