[EM] IRV vs Plurality (back to the pile count controversy)

[Abd ul-Rahman Lomax]

At 03:57 AM 1/22/2010, James Gilmour wrote:
>This
>second set of rules are those that prescribe the transfer of votes 
>"to the bitter end", i.e. even after the winners have all been
>determined.  Under this rule a ballot marked "A" would be treated 
>differently from a ballot marked "A>B": at the last possible
>transfer, the "A" ballot would become 'non-transferable 
>(exhausted)', but the "A>B" ballot would be transferred to A.

You mean transferred to B, of course.

>This second rule is, of course, a stupid rule but that does not mean 
>it has not been implemented in some jurisdictions, including,
>sadly, Scotland.

Not stupid, precisely because of the difference between A>B and A. 
The former is an acceptance of the last listed preference, the latter 
is not. It makes a difference if a majority is required. Not if it is 
not, though it might make a difference with some methods. But not IRV.

>  It is also a highly undesirable rule because it means that my vote 
> could, in some circumstances, be transferred to
>the candidate I deliberately ranked last in the lowest possible 
>place, e.g. 12th out of 12 candidates.

Basically, if there are as many ranks as candidates, don't vote for 
that last one! That's your choice, unless full ranking is required, 
in which case you *can't* vote the truncated vote and it is 
irrelevant if it's counted or not.

>   Following on from the
>concept of 'Later No Harm' (which underpins the whole of contingency 
>voting, as in IRV and STV-PR), it is very important to be able
>to give a voter the absolutely assurance that under no circumstances 
>will her vote ever be transferred to the candidate she has
>ranked 12th out of 12.  Sadly, the stupid "transfer to the bitter 
>end" rule undermines this.

Only because of voter ignorance, an ignorance which has sometimes 
been encouraged by activists.

The ballot instructions should state that one should not rank any 
candidate one is not willing to support over alternatives. If there 
are twelve candidates on the ballot, and write-in votes are not 
allowed (is that the truth there)?, and a majority is not required, 
there should only be eleven ranks, not twelve. Otherwise the ballot 
encourages the behavior you don't like.

But with write-in votes allowed, you need twelve ranks to cover a 
single allowed write-in. So that's thirteen candidates. And then the 
ballot instruction is important, because otherwise voters will 
imagine they are voting maximally against a candidate with a ranking 
of 12th. Instead, in these conditions, it's a vote for a candidate as 
against any possible write-in, including one the voter might well 
have preferred if aware that a write-in candidate had a prayer.

You are right, there is a problem, but it isn't with the rule that 
continues to the end, it's with voter education. If a majority is not 
required, though, it's moot. But with better preferential voting 
methods than IRV, there is indeed a difference between A>B and A.

I'm not at all convinced that full ranking provides useful 
information beyond the first few ranks. With Bucklin, three ranks are 
pretty obviously enough. In reality, in Bucklin elections, udner some 
conditions, only a bit over 10% of voters even used additional ranks.

It's not about later-no-harm, it's about how much information the 
voters have. If they have a strong preference for a frontrunner over 
all others, truncating is a perfectly sensible vote. It gets even 
more sensible if it's a runoff system.

If your voting method does indeed require a majority, why in the 
world do you add that 12th preference? By adding it, you are 
contributing to the community acceptance of the result, by 
withholding it, you are asking for a possible second chance for your favorite.

If a majority is required, the absolute Later No Harm promise of IRV 
is false. That's been missed by focus on the method as deterministic.