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.

This method can be viewed as a variant of Improved Condorcet Approval.

Another method with the above properties is Majority Approval, Minimum Pairwise Opposition (MAMPO).

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.

All dominated candidates are eliminated, unless this would eliminate all the candidates.

Of remaining candidates, the one approved by the most voters is elected.

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

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

Links

 * Method is first proposed on EM, with properties proven (Jun 21 2005)
 * Mike Ossipoff names the method
 * Warren D. Smith describes other favorite betrayal compliant methods that use majority defeat disqualification - MDD-Range and MDD-Summed-Ranks