[EM] How to vote in IRV

[MIKE OSSIPOFF]

Chris:

You wrote:

Similar to the good Approval strategy "approve the candidate A you would 
vote for in FPP, plus all the candidates you like as much or better than 
A" as an IRV strategy guide is "vote in first place the candidate A you 
would vote for in FPP and in second place the candidate B that you would 
vote for in FPP if A wasn't on the ballot and in third place the 
candidate C you would vote for in FPP if neither A or B was on the 
ballot, and so on."

[endquote]

Yes, that's a reasonable approximation.
 
You continued:

So barring rare and risky Push-over strategy opportunities, I don't see 
how IRV voting strategy is qualitatively more difficult than FPP strategy.

[endquote]

But, strictly speaking, it _is_ more complicated, because, in Plurality
it's just a matter of which acceptable candidate is most likely to be the
best votergetter. The popularity-measure for ranking the acceptables in
IRV will be more complicated.

 
> When there are completely unacceptable candidates who might
> win (I call that condition u/a, for “unacceptable/acceptable”)
>
> IRV, like many methods, has a relatively simple strategy:
 
You replied:
 
When the voter's over-riding priority is to prevent the election of an 
unacceptable candidate, the voter should rank the acceptable candidates 
in order of estimated pairwise strength versus the likely unacceptable 
finalist (i.e. the unacceptable candidate that isn't eliminated before 
the final virtual run-off).

[endquote]

But are you sure that it isn't more complicated than that. What about
pairwise strength against the 2nd most likely unacceptable finalist. What
about the ability to accumulate enough votes to even be a finalist?
No, it's more complicated.



You wrote:
  
There is no reason at all to not rank the unacceptables sincerely. If 
your ranking among the unacceptables is ever counted it means that your 
strategy (aimed at preventing the election of an unacceptable candidate) 
has failed, and if any are even slightly less bad than the very worst 
you might as well help the lesser evil (unless you are concerned about 
your vote's symbolic gesture and want to deny any unacceptable winner 
"legitimacy").

[endquote]

I agree with that. Strictly speaking, you gain some by ranking the
unacceptables too. I merely meant that the matter of which unacceptable
wins is far less important than the matter of whether the winner is
an acceptable or an unacceptable. So the somewhat more complicated
determination of unacceptable ranking order can reasonably be
ignored.

 
> What’s that you say? You might get lucky, even if you don’t
> top-rank a compromise?
 
You continued:

I think it is at least as easy to argue that 
Approval is "a game of chance".

[endquote]

How so?

Maybe you just mean that all strategy under uncertainty
is a "game of chance".

But I meant "game of chance" in a stronger sense.

In Approval, if you choose to vote a certain candidate-set over all the
other candidates, then it's certain that you're voting every candidate
in that set over all the candidates outside of that set. 

So Approval is incomparably more responsive than IRV. 

And the matter of which candidate(s) you're giving your vote to has
nothing to with chance. You, and only you, decide that and establish
it explicitly on your ballot.

It's in that sense that IRV is a game of chance, where Approval is not
a game of chance. 

Vote your favorite in 1st place and your needed compromise in 2nd place?

You can only guess and hope that you'll get to give vote to your compromise,
who may very well need it, and not get it. A game of chance.

Mike Ossipoff