The way that MCA works is quite simple: Give each candidate one of 3 ratings: Preferred, Acceptable, Unacceptable.
The person rated as "Preferred" by the largest number of people wins IF HE IS RATED PREFERRED BY A MAJORITY OF THE PEOPLE SUBMITTING BALLOTS. (Other cutoffs are also possible, but majority is the most commonly discussed cutoff.) If nobody is rated "Preferred" by a majority of the voters then we elect the person rated "Unacceptable" by the fewest people, or, equivalently, the person rated "Preferred" or "Acceptable" by the largest number of people. You gave this example: >51 ABC >49 BCA > >Using 50% as the percentage Favored votes required for a win, A would win >with MCA. > >However, it would be natural to assume that the opposite of Favored is >Unapproved. That is, MCA has levels that are like a 3-level Cardinal >Ratings system with each Favored vote getting +1 and each Unapproved vote >getting -1. Therefore, each Compromise vote should get 0. Using this, B >would be the winner. I'm not sure where you're going with this Cardinal Ratings analogy. Under reasonable assumptions about polling and voter behavior the winner would be A, since in such a case we can assume that the ABC voters would only rate A "Preferred." Sure, B could win if enough of the ABC voters also rated B as "Preferred" but that is unlikely, unless it's so close that polls cannot definitively say before election day which faction is larger AND the BCA faction rates both B and C as "Preferred." In that case, the ABC voters might hedge their bets against B and C both getting majorities by rating B as preferred. But, remember that a lot of assumptions went into this scenario where B wins. Relax any one of them and A will win. Alex ---- For more information about this list (subscribe, unsubscribe, FAQ, etc), please see http://www.eskimo.com/~robla/em
