[EM] Range Voting "unbeatable"?

[Warren Smith]

> "utterly false" is a bit strong language

--No: "absolutely" "unbeatable" is what is "strong language."
And it is false.   And what really pisses me off, is you accusing me of
being false, when it was you all along being false, and indeed I had
publicized the exact opposite of what you falsely said and falsely
attributed to me.    The correct response is
to apologize (jerk), not to come back accusing me of "strong
language"! Holy cow!

> I completely reject your model of strategic voters. It is simply not true that, if you surveyed all voters their honest opinions of who the two "frontrunners" are, all of them would agree in 100% of elections.

--Ok, the truth is not 100%, it is "over 98%."
Indeed, it is possible (proven by test) to predict all important US
races with >98%
accuracy over 1 year ahead of time.  Proof:  see remarks on Ron Facheux here:
http://www.rangevoting.org/NonVoters.html
Also: note the percent of third-party winners in the USA in such races
is below 1%.

OK.  Now, is this difference between 100 and 99% really a good basis
for your "complete rejection"?  Golly.  Gee willickers.  Total
unrealism!  You ARE finicky.

>I propose (and you have not responded) a different model of strategy.
1) Choose an underlying voter utility model which behaves roughly like
reality. This is an area for research, and my own incomplete ideas
don't fit here...

--actually, I already did this, and did it before you came along and
said this.
(See a common theme?  'Cause I'm noticing one.)
IEVS already includes "reality-based utilities" based on a dataset of
real world elections.
It turns out, when you run the experiment, that using reality-based
utilities leads to little-to-no discernible difference in results,
versus using fantasy-based utilities like
I had before.

>I can make Range behave like "random candidate" by assuming that candidate X's voters strategically bullet-vote and all other voters vote honestly. (For infinite numbers of voters in RNEM, you just assign a random epsilon(k) fraction of bullet voters to each kandidate, and then whichever one has the highest epsilon(k) wins.) Both assumptions are unrealistic worst-cases but arguably a significant drain factor on the systems' overall quality.

--this seems unlikely to be a realistic model. But if you think it is
realistic, then fine.
Put it in IEVS, and compare range to other voting systems under that model.
In particular, under the very model you just proposed, you will find
that Condorcet
systems also elect the highest-k guy.   Congratulations. You just
proposed a new model and found range and Condorcet and random
candidate all behaved the same under that model.   Which is fine, but
seems little basis for "[range] is not as great as you depict it."
I mean (since you seem to be a Condorcet supporter?) wouldn't it be a basis
for saying Condorcet is not as great as YOU depict it?



On 8/30/09, Jameson Quinn <jameson.quinn at gmail.com> wrote:
> 2009/8/30 Warren Smith <warren.wds at gmail.com>
>
>> >> Warren defines BR in such a way that Range is unbeatable
>> >> given sincere votes.
>> > Absolutely...
>>
>> --Sorry: these claims, although stated with the utmost apparent
>> confidence by their authors, are utterly false.   Range voting is
>> beatable, and has been beaten, with honest voters -- and I was the one
>> who did that!
>
>
> It's a nice result, but it relies completely on the specific probabilities
> derived from a perfect knowledge of the underlying voter model. So "utterly
> false" is a bit strong language. It would be possible to create voter
> models
> to satisfy any given "reweighting scheme" like the one you used, including
> the null-reweighting of vanilla Range. And if you want to talk about
> cross-model performance, you need metrics - I suspect that you're right,
> the
> most natural metrics do not favor Range, but a metric could certainly be
> constructed to favor Range.
>
>
>>
>> Further, certain systems also beat range voting with *strategic*
>> voters, for example
>> range+top2runoff system with 2 rounds beats plain range (i.e. has
>> lower BR) if there are about 75% or more strategic voters in the mix.
>
>
> I completely reject your model of strategic voters. It is simply not true
> that, if you surveyed all voters their honest opinions of who the two
> "frontrunners" are, all of them would agree in 100% of elections. Empirical
> evidence suggests otherwise even in plurality systems (sometimes major
> parties break down, sometimes voters are honestly deluded); and it is
> certainly arguable that this would be even less true in other systems. The
> paper you referenced shows that Plurality is especially bad in that it
> suffers a "phase transition" with any epsilon of strategic voters (and, by
> extension, if the group of strategic voters who believe in any given
> candidate is one of the frontrunners is larger than the group for any other
> candidate); in the real world, where a non-0 number of voters are
> intrinsically honest, you have not shown that your simplistic "two
> frontrunners" model for voter strategy is any kind of equilibrium strategy.
>
> I propose (and you have not responded) a different model of strategy.
>
> 1) Choose an underlying voter utility model which behaves roughly like
> reality. This is an area for research, and my own incomplete ideas don't
> fit
> here, but suffice it to say that the RNEM is not good enough (for instance,
> as you point out, it has a majority-top winner with 0 probability, whereas
> empirically it's closer to 50%).
>
> 2) Create virtual electorates and conduct "polling" in which a sample of
> the
> electorate gives their randomly-truncated ranked preference list.
>
> 3) Create (by hand or using genetic programming) and test "strategy
> heuristics", by which a given voter can use the polling (and knowledge of
> the underlying probabilistic models) to estimate the expected value of
> various strategic options, assuming all similar voters use the given
> strategy, and assuming no counterstrategy or defensive strategy.
>
> 4) Each voter has a strategy threshold - they will use a strategy if the
> expected value is above the threshold.
>
> 5) Run the election and measure BR
>
> 6) For a sample of elections, evaluate whether counterstrategy would be
> effective. Hopefully, for most good election systems and strategic
> thresholds, this will be a negligible effect.
>
> 7) If counterstrategy is not negligible, try to find the
> (perfect-information - not poll-based) Nash equilibrium for some simple
> cases with the fraction of strategic voters observed in 4 and 5. (This
> could
> be either a degenerate "two frontrunner"-type equilibrium, or some mix of
> honesty, strategy, and counterstrategy)
>
> This is a significant amount of work per voting system evaluated, but
> Condorcet methods generally would probably have similar results, so two of
> them would not be twice the work, while several other systems would be
> strategically degenerate (I suspect Range->Approval and
> {IRV,Borda}->Plurality for all strategic voters).
>
>
>>
>> Range+top2runoff does beat range if the strategy-fraction is large, but
>> it
>> doesn't beat it by much (10-30% regret reduction); meanwhile range
>> beats range+top2runoff by a lot more than that if the honesty-fraction
>> is large.
>>
>
> Again, this is totally dependent on your definition of "strategy".
>
>
>> So in view of this, at present I still think plain range voting is a
>> pretty good choice.
>>
>
> I agree. But it is not as great as you depict it. Just as you can make any
> Condorcet system behave like Plurality by assuming 2 frontrunners and 100%
> strategy, I can make Range behave like "random candidate" by assuming that
> candidate X's voters strategically bullet-vote and all other voters vote
> honestly. (For infinite numbers of voters in RNEM, you just assign a random
> epsilon(k) fraction of bullet voters to each kandidate, and then whichever
> one has the highest epsilon(k) wins.) Both assumptions are unrealistic
> worst-cases but arguably a significant drain factor on the systems' overall
> quality.
>
> Jameson
>


-- 
Warren D. Smith
http://RangeVoting.org  <-- add your endorsement (by clicking
"endorse" as 1st step)
and
math.temple.edu/~wds/homepage/works.html