Majority Choice Approval: Difference between revisions

'''Majority Choice Approval''' ('''MCA''') is a class of rated voting systems which attempt to find majority support for some candidate. It is closely related to Bucklin Voting, which refers to ranked systems using similar rules. In fact, some people consider MCA a subclass of Bucklin, calling it [[ER-Bucklin]] (for Equal-Ratings-[allowed] Bucklin).

There is no preferred majority winner. Therefore approved votes are added. This moves Nashville and ChatanoogaChattanooga above 50%, so a winner can be determined. All the given resolution methods would pick Nashville, which is also the [[pairwise champion]] in this example.

Various strategy attempts are possible in this scenario, but all would likely fail. If the eastern and western halves of the state both strategically refused to approve each other, in an attempt by the eastern half to pick ChatanoogaChattanooga, Nashville would still win. If Memphis, Nashville, and ChatanoogaChattanooga all bullet-voted in the hopes of winning, most Knoxville voters would probably extend approval as far as Nashville to prevent a win by Memphis, and/or at least a few Memphis voters (>8% overall, out of 42%) would approve Nashville to stop ChatanoogaChattanooga from winning. Either one of these secondary groups would be enough to ensure a Nashville win in any of the MCA variants. It would take a conjunction of four separate conditions for ChatanoogaChattanooga to plausibly win: it could happen only if Knoxville voters also preferred ChatanoogaChattanooga, and Nashville voters (un-strategically) approved ChatanoogaChattanooga, and no Memphis voters preferred Nashville, and the MCA-P variant were used.

If the electorate knows which two candidates are frontrunners, and the pairwise champion is indeed among those two, the stable strategy is for everyone to approve or prefer exactly one of those two, and fill out the rest of the ballot honestly and as expressively as possible. (In the example above, that would mean an east/west split, with Nashville winning 68-32 approval over ChatanoogaChattanooga.) If everyone follows this strategy, the pairwise champion will win with the only absolute majority. And if even half of voters follow this strategy, multiple majorities are highly unlikely.

However, this two-frontrunner strategy does not mean that MCA is subject to [[W:Duverger's law|Duverger's law]]. A pairwise champion who is not one of the perceived frontrunners still has a good chance of winning, especially if they have some strong supporters. This fact, in turn, will affect what "frontrunner" means; an extremist candidate with a strong but sharply-limited base of support - the kind of candidate who, using simple [[runoff voting]], makes it into a runoff with a strong showing of 35% but then gets creamed with only 37% in the runoff - will never be perceived as a frontrunner in the first place.