[EM] IRV vs Plurality

[Stéphane Rouillon]

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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