Legitimacy of collective decisions: a mechanism design approach

TL;DR

This paper introduces two innovative mechanisms for collective decision-making that guarantee the majority preferred option wins in all equilibria, improving on existing methods by ensuring truthful voting and efficiency.

Contribution

It presents novel mechanisms that ensure majority rule implementation in all equilibria and reduce the steps needed for correct outcomes, addressing limitations of previous approaches.

Findings

Mechanism 1 allows agents to choose cooperation partners, overcoming impossibility results.

Mechanism 2 uses sequential ratification to reach outcomes faster.

Both mechanisms incentivize truthful voting through off-equilibrium lotteries.

Abstract

We design two mechanisms that ensure that the majority preferred option wins in all equilibria. The first one is a simultaneous game where agents choose other agents to cooperate with on top of the vote for an alternative, thus overcoming recent impossibility results concerning the implementation of majority rule. The second one adds sequential ratification to the standard majority voting procedure allowing to reach the (correct) outcome in significantly fewer steps than the widely used roll call voting. Both mechanisms use off-equilibrium lotteries to incentivize truthful voting. We discuss different extensions, including the possibility for agents to abstain.