The methods are quite different in the case where it is sufficient to
*weaken* the strength of the A>B win without needing to reverse it.
In WV and MMPO (that is, MinMax(pairwise opposition)), there is never
favorite betrayal in this case, because changing the vote A>B to A=B is
no more effective than changing it to B>A. Every voter making this change
reduces the A>B strength by 1 vote.
But in margins, favorite betrayal always works twice as fast as equal
ranking. Changing A>B to A=B shrinks the margin by 1 vote, while changing
it to B>A shrinks the margin by 2 votes. Sometimes B>A is going to be the
only way to weaken the defeat sufficiently.
In DMC, neither A=B nor B>A is effective. The only ability you have to weaken
the A>B win (assuming you can't reverse it) is to disapprove A!
This seems to imply the possibility of favorite betrayal in a pretty common case. Say your sincere ranking was A>B>cutoff>C. Furthermore, assume that your approval of B is important to maintaining the strength of the B>C defeat. If it was necessary to reduce the strength of the A>B win, wouldn't the necessary strategic vote then become B>cutoff>A>C, i.e. favorite betrayal?
(My FBC simulation doesn't envision favorite betrayal of that kind, so I
would have to rethink it in order to find statistics for DMC relative to
WV and margins.)
I think that would be worth looking into. My guess (and I stress that it is only a guess) is that DMC would have favorite betrayal incentive less often than margins, but significantly more than wv.
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