[EM] Why I think IRV isn't a serious alternative 2

Kevin Venzke stepjak at yahoo.fr
Sat Dec 13 17:57:52 PST 2008


Here are some sections I wanted to quickly reply to.

--- En date de : Lun 8.12.08, Abd ul-Rahman Lomax <abd at lomaxdesign.com> a écrit :
>> What you're talking about here isn't even "playing nice," it's more
>> like using lower ratings as loose change to toss into an (inadequate)
>> street musician's hat. I'm not clear on what motivates that either.
>> I don't think I've ever wanted to communicate to a candidate that they
>> aren't acceptable (i.e. worse than what I expect out of the election
>> after considering both frontrunners' odds), but should keep trying.
>Why did voters vote for Nader in 2000? Were they purely stupid? You may >never have voted this way, but other real people do. Why do voters bother >to vote for minor parties, ever? Do you think that most of them imagine >that candidate could win?

I would say that they voted for Nader because they wanted him to win. It
is not relevant whether he could or not. The phenomenon I'm scratching
my head over, is where you give a lowish but positive rating to someone
who isn't good enough to be elected, but good enough to "encourage" in
a sense.

>> I'd rather "start" with MCA (two rating levels plus the option to
>> not rate at all) and stay there, as I think MCA is at least a little
>> better than Approval.
>How is it counted?

There are three slots (the lowest of which can be expressed through
truncation). If any candidate has top-slot ratings from more than half
of the voters, then the one of these candidates with the most, wins.
If there is no such candidate, then elect the candidate who has the
most top-slot plus middle-slot ratings. (Which is the same as saying:
Elect the candidate truncated by the fewest voters.)

I have criticized this method (and Bucklin and median rating, to which it
is similar) for not offering any great basis on which to decide whether
to rate a candidate top or middle. But I do guess that it is more stable
and more Condorcet efficient (in the abstract sense) than Approval. (In
my simulations it was definitely more stable, though it was difficult
to devise the strategic logic for it, so there could have been a flaw.)

>> That's not very generous. I can think of a couple of defenses. One would
>> be to point out that it is necessitated by the other criteria that IRV
>> satisfies. All things being equal, I consider LNHarm more desirable than
>> monotonicity, for instance.
>I, and certainly some experts, consider LNH to cause serious harm. 
>Absolutely, it's undesirable in deliberative process, someone who insists 
>on not disclosing lower preferences until their first preference has 
>become impossible would be considered a fanatic or selfish. That's a 
>trait I'd like to allow, but not encourage!

Well, I said "all things being equal." All things being equal I think it
is a positive thing that by providing more information, you don't have
to worry that you're worsening the outcome for yourself. Maybe something
else gets ruined, but then all things are not equal.

Again, you seem to describe LNH as though it is synonymous with the IRV
counting mechanism. MMPO and DSC do not render preferences "impossible"
thereupon "disclosing" more preferences.

>Entirely neglected in Kevins consideration here is the possibility I've 
>mentioned: that the very fact that voters can express intermediate 
>ratings, and the near certainty that some do so, improves the method 

There is a possibility. But even if voters do provide them, this isn't
sufficient to say that this would improve method performance, because we
can't deduce that the intermediate ratings we collect mean the same thing
as the mind-read utilities we can see in simulations.

>> Warren's approach could be useful when:
>> 1. they simulate realistic voter profiles (and some of them apparently 
>> but again, anyone can argue about whether they really are realistic)
>I've pointed out that they don't have to be realistic, only unbiased, not 
>warped against one method and for another.

I don't agree. If certain scenarios are realistic for public elections,
then those are the profiles we care about.

The idea of scoring each method according to an average of all possible
election scenarios, is not on its face very promising.

>> 3. they simulate voter strategy that is customized to the method
>That is relatively easy, and has been done.

No, this is the hard one! I don't know if Warren has even implemented
this for Approval and Range. I don't remember, whether the strategic
voters simply exaggerate, or actually approve above-mean.

For rank ballot methods Warren has implemented the same strategy for all,
and it is the biggest problem, with the least clear solution.

>> 4. they simulate pre-election information
>This is necessary for Approval and Range strategy, for sure, so I believe 
>this has been done. 

I don't believe Warren's simulations do this for any method. All
strategy is either zero-info, or (for rank ballot methods) based on
random arbitrary info provided uniformly to all voters.

>It can actually be done, in the simulations, with perfect strategy, 
>though, obviously, if you take this too far, you could run into loops, so 
>I'd guess that the best strategy used would assume some uncertainty and 
>would only iterate so many times, simulating polls and then shifts in 
>votes as a result, then another poll, etc. The "polls" would solicit how 
>the voter intends to vote, and the model can assume that the voter can't 
>hide the information. After all, just how complicated do we want to make 
>the model?

Yes, my simulations are based on polls. Polls are a great idea.

How complicated do we want to make the model? Sufficiently complicated
that we can compare methods in realistic situations. Personally I only
care about public elections.

>Heavy use of serious strategization is pretty unlikely with ranked 
>methods, in my opinion, most voters will simply do as the method implies, 
>rank in preference order, and they can do this a bit more easily if equal 
>ranking is allowed.

Warren's implementation would suggest that he strongly disagrees with you
on this.

>> Some of this isn't difficult, it's just again a question of how far you
>> take it. Strategic voter behavior needs to be made less ridiculous.
>> But what kind of strategy should be allowed, for (let's say) Condorcet
>> methods? If everyone votes sincerely, then Range will look bad. So
>> clearly the line has to be drawn somewhere else.
>No, you'd have to compare sincere Condorcet with some kind of sincere 

Look at it this way: To compare methods fairly we need to know how
strategic voters attempt to be, in the same situations, under whatever
methods we want to compare. Why compare strategic Method A with strategic
Method B, if Method B voters would never vote that way in reality?

What if, in real life, Condorcet voters just don't use any strategy?
And what if it's also true, that Range voters in real life turn the
method into Approval? In that case, the only useful comparison to be
done by the simulations, would happen to be sincere (or strategic, no
difference) Condorcet vs. strategic Range/Approval. And according to
Warren's simulations, Range doesn't win, in that case.

>> I wonder if you have ever been curious to wonder what a "strategic" 
>>voter is, for a rank ballot method.
>Nah, curiosity killed the cat.
>I've done a fair amount of reading on this, but who remembers anything? 
>Often not me.

Actually this question was specifically about the simulations.

>> Some six months ago I wrote a strategy simulation for a number of
>> methods. One situation I tested was Approval, given a one-dimensional
>> spectrum and about five candidates, A B C D E.
>> In my simulation, once it was evident that C was likely to win, one of
>> either B or D's supporters would stop exclusively voting for that
>> candidate, and would vote also for C.
>B and D voters are motivated to ensure that C wins if their favorite 
>doesn't. Hence Approval will tend to find a compromise. If B or D are not 
>relevant, can't win, they *may* also vote for B or D, so I'm not sure 
>that the simulation was accurate. 

I'm not sure what you mean by this. Voters that prefer B or D to C have
no reason to not continue voting for B or D.

The issue is that when all the D supporters (for example) *also* vote
for C, then it isn't possible for D to win. And the more that D voters
"give up" and vote for both, the less sense it makes strategically for
the remaining D-only voters to not "give up" as well.

>The vote would depend on preference 
>strenth in the pair involving C and their favorite. If weak, more likely 
>to also approve, but, note, this doesn't, by definition, affect the 
>outcome unless they have bad information.
>In a real situation, the likelihood of bullet voting varies with utility 
>distance, i.e, preference strength. If we look at a voter equidistant 
>between B and C, the voter may actually have minimal preference between B 
>and C and even have difficulty deciding which to vote for as a first 
>preference. For some region between B and C voting for both in Approval 
>will be common.

My simulations involve polls. When the polls find that the winner will
either be B or C, then it's strategically unwise to not approve one of

At first, the polls report that C will win a lot but (due to bullet
voters for B and D) there is some chance that B or D will win. Eventually
the polls (which are subject to some randomness) will produce a prediction
that D's odds (or B's) are abnormally poor. This causes D voters to stop
voting only for D, and also vote for C. This almost immediately makes D an 
unviable candidate, and the bullet voters for D disappear.

Kevin Venzke


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