Majority Defeat Disqualification Approval

Majority Defeat Disqualification Approval or MDDA is a method devised by Kevin Venzke for the purpose of showing that the Favorite Betrayal criterion, Strategy-Free criterion, and Strong Defensive Strategy criterion are mutually compatible. The name was given by Mike Ossipoff.

Procedure

The voter submits a ranking of the candidates. The candidates explicitly ranked are considered approved by that voter.

A candidate is dominated if more than half of the voters rank some other candidate strictly above him.

Sort the candidates so that all undominated candidates, if any exist, come before all dominated candidates. Within each group, sort of the candidates in descending order of approval.

Elect the first candidate in the resulting ranking.

Criteria

MDDA satisfies the Favorite Betrayal criterion, Strategy-Free criterion, the Strong Defensive Strategy criterion (and Minimal Defense criterion), monotonicity, and (check this) the Plurality criterion.

It fails Clone-Winner, the Generalized Strategy-Free criterion, the Condorcet criterion, the Smith criterion, Participation, the Majority criterion for solid coalitions, and Later-no-harm.

Work in progress.