[EM] IRV nonmonotonicity examples

[MIKE OSSIPOFF]

We have two IRV nonmonotonicity examples at

http://www.electionmethods.org

One uses only a few candidates. Another, originally from Brams,
is one in which a candidate was going to win, but then some people
who'd intended to rank him in last place decide instead to rank
him in 1st place. That causes him to lose.

A scarier version of that example is one in which a candidate is
going to lose, but then his extreme corruption is discovered, and
many people who were going to rank him 1st decide instead to rank
him last, and that causes him to win.

Corruption disclosures shouldn't make a candidate win.

You might also consider the simple but convincing Participation
Criterion:

Adding to the count one or more ballots that vote X over Y should
never change the winner from X to Y.

[end of definition]

Say nearly everyone has voted, and they've voted like this:

35: ABC
33: BAC
32: CBA

C gets eliminated and the C votes transfer to B, who wins.

But, just before the polls are closed, 2 more voters decide that
they should vote too, so that they can do their part to at least
ensure that their last choice won't win. They vote CBA.

Because they showed up and voted, they changed the winner from B to
C, their last choice.

Mike Ossipoff




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