[EM] IRV vs Plurality

[Abd ul-Rahman Lomax]

At 01:06 AM 1/10/2010, Jonathan Lundell wrote:
>On Jan 9, 2010, at 9:23 PM, Abd ul-Rahman Lomax wrote:
>
> > 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.
>
>It's hard to know what to make of this claim, other than, "so what?" 
>-- if what you're comparing to TTR is the IRV candidates with the 
>highest first-choice ballots.

I'm comparing *elections*. Yes, not all questions are addressed, but 
the response of "so what?" misses the point, obviously. If we assume 
sincere voting in TTR and IRV, and if we consider real world 
conditions (separate runoff, not merely some simulated runoff with 
the same voters and the same preferences and no new knowledge or 
shift of preference or better consideration, etc.), the results are 
quite different. That preference order doesn't shift in nonpartisan 
IRV elections, though the vote transfer process, was completely 
unanticipated, as far as I know. Mr. Lundell, were you aware of it? 
Did anyone predict this?

What this means that, with very little exception, you can use 
Plurality instead of IRV. And this just may explain why Plurality has 
remained so popular for so long. In certain contexts, it works quite well.

>Presumably voters in TTR and IRV elections know the counting rules.

No. We can't presume that, in fact. Both TTR and IRV generally 
encourage sincere first-preference votes, not in reality, but in 
appearance. I believe that most votes in the current IRV elections in 
the U.S. are quite sincere, they aren't being gamed, as they would 
need to be to maximize voter expected satisfaction, in some cases. 
With TTR, indeed, voters may know the rules. They might even know IRV 
rules, but the *implications* of the rules, that knowledge, from what 
I've seen, is unusual.

>  The meaning of a first-choice IRV vote is not the same as a TTR 
> first-round vote. One plausible interpretation: if a TTR primary 
> results in A>B, A tends to have all the votes A is ever going to 
> get, but B, in the runoff, gets all the "anybody but A" votes, and wins.

When there is a runoff between two candidates, there is much closer 
examination of the two candidates. Further, preference strength 
enters into runoffs, causing results to shift toward what would be 
range voting results. Sincere range voting! I'm assuming, here, that 
the runoff is a special election. If the primary is the special 
election (seems to be common in North Carolina, for example), then it 
is the primary results that are range-shifted. That's improved 
election quality, Johathan. People vote when they care. We cannot 
tell from low turnout if the turnout is low because voters are 
equally disgusted with both candidates, equally pleased, or truly 
don't care about who wins no matter who the candidates are. High 
participation in a general election means a lot of noise, voters with 
low preference strength (which may be due to lack of knowledge, or 
may be intrinsic, i.e., they *do* know the candidates and don't care 
which one wins).

The proposed explanation for comeback elections, however, "anybody 
but A," is probably rare. Much more likely is this, as one example:

B is a dark horse, wasn't expected to do as well as actually 
happened. When B makes it into the runoff, suddenly those who 
supported B or who would have supported be had they known about B, 
will turn out to vote. In the other direction, those who voted in the 
primary and who actually have low preference between A and B may not 
turn out to vote; perhaps A was better known and got votes from these 
voters. So A may lose votes and B may gain them. Add to this the 
effect of additional campaigning, where B, now being a serious 
contender, gains more funding and more explicit support, perhaps the 
recommendation of other candidates.

Whether or not all this is likely may depend on the margin, but if B 
was truly a dark horse, B stands to gain votes from those who voted 
for other candidates. To me, the really interesting situation is 
where a center squeezed candidate doesn't make it into the runoff. 
What were the vote margins? Are there signs that the eliminated 
candidate was actually the Condorcet winner? By what margin and what 
preference strength? These would be factors in determining if a 
write-in campaign is appropriate. Using an advanced method in the 
runoff, even if there are only two candidates on the ballot, and 
allowing write-ins, allows fixing this problem with top two runoff! 
And the problem is less likely to arise if an advanced method is used 
in the primary as well.


>OTOH, A>B>... in the first round of an IRV election tells us 
>considerably less, since the cost of voting for a non-poll-leader is 
>considerably less than with TTR. It's entirely plausible, though of 
>course not necessary, that the A:B first choice breakdown reflects 
>the lower-choice breakdown of the other voters.

This is what we see in IRV elections, when they are nonpartisan. It 
is as if the supporters of each candidate as most-preferred are a 
sample from the same population that is otherwise similar. So if, 
say, those who prefer someone other than A are considered as to their 
preference for B>C, the ratio of B>C preferences will be the same for 
those who prefer A. This was unexpected, to me, but it does make some 
kind of sense.

Most of our thinking about voting systems has been colored by 
thinking in terms of factional preferences, which are roughly 
predictable and not at all like this. We expect that a Progressive 
voter in Burlington will be more likely to support the Democrat over 
the Republican, and by significant margins, and we likewise expect 
that a Republican voter will be more likely to prefer the Democrat 
over the Progressive. In Burlington, the Democrats are in the middle, 
the center, they are the local moderates.

But nonpartisan elections don't seem to work like this. They are 
about personalities, less about issues and general stances on issues, 
I suspect. They may be about perception of trustworthiness.