[EM] Methods of elimination in quota preferential STV

[MIKE OSSIPOFF]

Craig Layton wrote:

Oh, and in regards to the question of strategic voting; strategic voting (to
the extent that it effects large scale elections) seems to be extremely
unlikely in every system but plurality (where it occurs at every election).
Perhaps the current omnipresence of strategic voting has made this seem much
more of a likelyhood than it really is.

I reply:

Ok, say therea are 3 candidates, Favorite, Middle, & Worst. You
like them in an order that accords with their names.

Say we know that the candidates' 1st choice support is roughly equal,
and that the Middle voters will rank Worst as their 2nd choice.

Other than that, we don't know what will happen or what the relative
numbers are. But we do know, because of the rough equality of the
3 candidates, that no candidate has a 1st choice majority.

What, then, would you, as a Favorite voter, do, in IRV (aka
the Alternative Vote, PV (single-winner), MPV, etc.)

Would you rank sincerely? Why? You know that Favorite can't win.
He hasn't got a majority, and the Middle voters are going to transfer
the other way if Middle is eliminated. You gain absolutely nothing
by ranking sincerely instead of ranking Middle in 1st place.

If you rank Middle in 1st place, you can keep Middle from getting
eliminated and electing Worst.

The strategy of voting sincerely is "dominated" by the strategy of
voting for Middle in 1st place, given what we know about the
election. Voting Middle can get you a better result than voting
sincerely, but sincerely can't give you a better result than voting
Middle in 1st place.

The rational strategy, then, for the you, if you want to optimize
his outcome for the current election, is to vote Middle in 1st place.

Are you sure that Australian voters don't talk about that kind of
voting? An Australian on this list once told us that small parties
there have as difficult time convincing their members to sincerely
rank their own small party candidate in 1st place, in IRV elections,
because those voters want instead to vote a lesser-evil, one of the
big-2, in 1st place, to protect a perceived needed compromise.

Mike Ossipoff








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