[EM] IRV vs Plurality

[Terry Bouricius]

Stephane,

Although Abd often asserts that IRV replicates FPTP results, I don't think 
he is claiming that in the last Burlington election. The plurality leader 
was the Republican Kurt Wright with 33%. He presumably would have won 
under FPTP. However, as the weaker candidates were eliminated (first the 
Green and Independent, and then the Democrat) the Progressive Party 
incumbent mayor who was in second place in the initial first-choice tally 
won the runoff.

Of course, there is the additional factor that a change in voting rules 
would likely change both campaign tactics as well as fears about spoilers, 
and whether all five candidates would have even run. It is certainly 
possible that the Democratic Party candidate would be dismissed as a 
"spoiler" with the Republican challenger and Progressive incumbent being 
seen as the "credible" candidates. It is also quite possible that the 
Independent with around 10% first choice support would not have run if 
FPTP had been used. Voters rather universally ranked their true favorite 
choice as number one, but that wouldn't have been true under FPTP.

IRV resulted in a VERY different set of dynamics than would have existed 
with FPTP, so it is impossible to say with any certainty what the outcome 
would have been. It is also noteworthy that the current debate is NOT 
about substituting typical FPTP, but rather FPTP with a 40% requirement. 
Under that scenario, it is quite likely that the Progressive would have 
won as well, since no candidate reached 40% initially, and IRV replicated 
the likely runoff outcome.

Terry Bouricius


----- Original Message ----- 
From: "Stéphane Rouillon" <stephane.rouillon at sympatico.ca>
To: "Abd ul-Rahman Lomax" <abd at lomaxdesign.com>
Cc: <kathy.dopp at gmail.com>; <election-methods at lists.electorama.com>
Sent: Sunday, January 10, 2010 1:57 PM
Subject: Re: [EM] IRV vs Plurality


Abd Ul,

from the data you produce, I agree that for the Burlington election, IRV
did produce the same result
FPTP would have produced.
However, nobody can generalize this perticular case to any election.
I agree that in non-partisan election the rallying pattern of defeated
voters does not fit only one typical set of preferences.
However again, a statistical analysis of general preferences shows an
unbalance of preferences, even for non-partisan elections.
Is this unbalance major to the point that IRV could allow a come-back
from another candidate than the plurality winner, or
is this unbalance minor so IRV does not change anything, it depends of
each election.
On a last aspect, I do agree that Condorcet is better than both. And I
admit that , even if I believe that the distribution
of a generalized set of preferences is unbalanced, I have not yet been
able to evaluate or quantify  this unbalance.

You can argue that as long that I was not able to quantify by how much
this unbalance occurs (amplitude distribution), it is not
acceptable to claim that this unbalance should allow IRV to find a
"better" winner. But, we do have data of previous elections and
because we both agree that a Condorcet winner is a "better" winner for
this purpose, we can use this reference to evaluate the
combined impact of IRV and the unbalance of the preference sets. Thus,
even if I do dot know the general unbalance distribution,
I can observe that IRV allows more often to obtain a Condoret winner
when plurality fails, than plurality finds a Condorcet winner
when IRV fails. So I claim IRV is more reliable than plurality.

Yours, Stéphane.

Abd ul-Rahman Lomax a écrit :
> At 09:23 AM 1/8/2010, Stéphane Rouillon wrote:
>> > Therefore IRV/STV is no better than plurality, but has extra very
>> > serious flaws, inequities, and vagaries that plurality does not have.
>>
>> I definitively disagree. Plurality is worst than IRV.
>> The flaws that IRV does have are real.
>> But these problems appear very less often than the splitting-vote
>> issue of FPTP.
>
> Stephane, as to abstract theoretical voting systems, naively analyzed,
> and also as to certain real-world situations -- but not others -- 
> you'd be correct. But notice that Kathy Dopp claimed that IRV is "no
> better than plurality." That's because, in nonpartisan elections, it
> appears that IRV closely reproduces the results of plurality. We have
> tended to think in terms of neat factions, arranged in a spectrum, so
> that you can predict vote transfer patterns with IRV, but nonpartisan
> elections don't work that way.
>
> Generally, in nonpartisan elections in the U.S., vote transfers with
> IRV do not alter the preference order among the remaining candidates.
> Exceptions may occur when races are very close.
>
> On the other hand, in one-third of nonpartisan top-two runoff
> elections, which IRV supposedly simulates, the runner-up in the
> primary goes on to win the runoff, a "comeback election," according to
> a FairVote study. It simply does not happen with IRV.
>
> If you have top-two runoff as a system in use, and you replace it with
> IRV, for nonpartisan elections, you might as well replace it with
> plurality, you will get the same results. That's what is being said.
>
> The recent election in Burlington, Vermont, though, was a partisan
> election. There, Kiss was trailing Wright in first-preference votes,
> but Kiss obtained enough vote transfers from Montrose supporters to
> pass up Wright in the second round of counting. Kiss is Progressive,
> Wright Republican, and Montrose is a Democrat.
>
> But looking at the actual voting data, which is available, we can see
> that Montrose was, in fact, the Condorcet winner, and, as it's been
> pointed out, had a few of the Write supporters voted for Montrose in
> first place instead of in second, Montrose would have won. In other
> words, IRV will punish you (as does plurality) for voting your
> conscience; but with Plurality, it's obvious and everyone would know
> that voting for a Republican in Burlington would be a wasted vote
> (where the leading party is Progressive), so they'd have compromised
> and voted accordingly and Montrose would quite likely have won.
>
> Also, there is good reason to believe that most voters would vote
> according to the same patterns if the method were Bucklin. The ballot
> would have been the same, three-rank. With Bucklin, first round
> results would have been same as IRV, presumably (and assuming that
> nobody did, with IRV, vote strategically already, we can assume that
> with the limited experience with IRV, few would have known to do so).
> Data is from a quite good video Kathy Dopp pointed to,
> http://www.youtube.com/watch?v=bPCS-zWuel8
>
> candidate       1st     2nd
> Montrose        2554    3556
> Kiss            2982    1827
> Wright          3297    1138
> ------------------------------
>                 8843    6521
>
> The ballots show third rank data, but my view is that this isn't
> meaningful, many voters may actually be thinking that they are voting
> *against* a candidate by ranking in third place. (There were other
> minor candidates on the ballot and the data in the video is obviously
> oversimplified, but it serves as an example.)
>
> As you can see, no candidate gained a majority in first preference.
> There is serious vote-splitting between Montrose and Kiss, quite
> likely. With IRV, Montrose is eliminated before the second rank votes
> for him are counted. That's 3556 votes that weren't counted!
>
> With Bucklin, all the votes are counted up to the ranks necessary to
> find a majority. The majority is 4422. Adding in the second rank
> votes, we get
>
> Montrose        6110
> Kiss            4809
> Wright          4435
>
> It's not even close! Montrose is the first or second choice of roughly
> three-fourths of the voters. This is Bucklin voting, supremely easy to
> count, just add up the expressed preferences at each rank. It's
> Instant Runoff Approval.
>
> It's true that there might not be such heavy usage of second rank with
> Bucklin (though already 2312 voters "truncated," not expressing a
> second preference). However, there are two possible ways to use Bucklin.
>
> We can generally assume that the votes in the Burlington election were
> sincere. They might not stay that way if Burlington Republican voters
> realize they've been had. Because there are no candidate eliminations
> in Bucklin, though, supporters of minor candidates can safely vote
> their conscience in first rank, because their vote will either help
> their candidate win (unlikely by the conditions) or will cause
> majority failure or will be moot in any case. There is no need for
> Favorite Betrayal, as it's called.
>
> What we have in Burlinton is a three party system, with the
> Republicans being, slightly, the largest. Naturally, they might prefer
> Plurality, except that they know they won't win, because they'd need
> more than a third of the voters. I'd expect Burlington to see a lot of
> runoffs if top-two runoff is used, straight.
>
> But consider top-two runoff with Bucklin used in the primary (and I
> believe that it would be wise to allow write-ins in the runoff and use
> Bucklin there too to prevent the spoiler effect).
>
> The voters would have -- would learn that they have -- a choice: add
> second rank (or third rank) votes if you approve of additional
> candidates, even though you have some stronger preference, or see a
> runoff election. The circumstances actually encourage a form of range
> voting, whether or not you'd add a second or third rank vote depends
> on *how much* you prefer your favorite over the others. This would
> amalgamate to show average preference strength against an actual
> inconvenience. In Bucklin, it's true, if your favorite doesn't win in
> the first round, your second rank vote can cause your favorite to
> lose. IRV allows you to think you are avoiding this possibly
> undesirable outcome, but only because it takes your candidate and
> eliminates him.
>
> Were the Wright voters in Burlington happy because their vote for
> Wright was "protected" from "hurting" Wright?
>
> The 2009 Burlington outcome was truly outrageous, and the votes show
> it. It was a classic center squeeze situation, and the possibility of
> this is precisely why Robert's Rules of Order criticizes IRV and
> considers true repeated balloting (without eliminations!) superior.
> RRO doesn't consider other forms of preferential voting though it
> notes that they exist. I understand that this is because RRO is a
> manual of actual practice, not of theoretical recommendations, but
> there are much, much better voting systems.
>
> Bucklin, to me, has these advantages:
>
> 1. It's been widely used in the U.S., about eighty years ago. It was
> very popular, and much more widely used than the current IRV fad. Why
> was it dumped? Good question. I wish I knew. Most likely answer: it
> worked, and some people didn't like that, such as the Minnesota
> Supreme Court.
>
> 2. It's cheap to canvass. Just add up votes, no complicated handling,
> totals can be summed by precinct easily and transmitted.
>
> 3. It preserves the ability to vote for more than one candidate but
> simultaneously indicate preference, unlike Approval. (Bucklin is
> really Approval voting with a "virtual runoff" feature, so that
> approvals are added in as needed.)
>
> 4. It satisfies the Majority Criterion, which is politically
> desirable. It does not satisfy, technically, the Condorcet Criterion,
> though my sense is that Condorcet failure would be rare and with low
> preference strength.
>
> Bucklin would have allowed the Republican voters in Burlington to vote
> for Wright without suffering the consequential loss of their second
> choice to their lowest preference. Someone should tell them!
>
> I think it's worth looking at how voting strategy might work. Some
> candidates might encourage their supporters not to add lower ranked
> votes for their major opponent. But we already see that many of the
> voters in Burlington did not vote the standard politically predictable
> patterns. We had some Wright supporters voting second rank for Kiss.
> Did that mean that they really preferred Kiss to Montrose. Maybe. Or
> they believed that this would somehow help Wright. Likewise, we had
> Kiss voters voting second rank for Wright. But in both cases these
> numbers were fairly small.
>
> I would indeed expect truncation to increase a bit with Bucklin, maybe
> even a lot. However, not enough, I'm practically certain, to alter the
> result. Second rank voting would have had to decline by 1689 votes for
> Montrose not to gain a majority, from his 3556 second-rank votes as
> shown. He'd still have a plurality. If a majority were required, he'd
> be in the runoff, certainly (whereas with a vote-for-one primary, he
> might be eliminated).
>
> If runoffs are held when there is majority failure, voters should know
> that they should not vote for a candidate, at any rank, unless they
> prefer the election of that candidate to a runoff being held (with its
> costs, inconvenience, and risks). Voters should also be able to leave
> lower ranks blank, deferring the counting of a lower ranked vote until
> later in the process. (It's a little more protection against "harming
> your favorite.") They should also be able to vote for more than one
> candidate at any rank, for reasons I won't explain here, but it is a
> good strategy if you really don't have a strong preference between two
> candidates. But, of course, they should never be able to vote more
> than once for any given candidate, should they mark the same candidate
> in lower ranks, those additional marks would simply be disregarded,
> they should not invalidate the ballot. A vote for a candidate will be
> counted at the highest rank expressed....
>
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