# Rank Maximal Equal Contribution: a Probabilistic Social Choice Function

## TL;DR

This paper introduces RMEC, a new voting rule that guarantees strong participation incentives and Pareto efficiency, while being computationally feasible and fair, advancing social choice theory.

## Contribution

The paper proposes RMEC, a novel probabilistic social choice function that ensures the strongest participation and ex post efficiency, with polynomial-time computability and fairness properties.

## Key findings

- RMEC satisfies the strongest participation condition.
- RMEC is ex post efficient.
- RMEC is polynomial-time computable.

## Abstract

When aggregating preferences of agents via voting, two desirable goals are to incentivize agents to participate in the voting process and then identify outcomes that are Pareto efficient. We consider participation as formalized by Brandl, Brandt, and Hofbauer (2015) based on the stochastic dominance (SD) relation. We formulate a new rule called RMEC (Rank Maximal Equal Contribution) that satisfies the strongest notion of participation and is also ex post efficient. The rule is polynomial-time computable and also satisfies many other desirable fairness properties. The rule suggests a general approach to achieving ex post efficiency and very strong participation.