[EM] IRV vs. plurality

[Adam Tarr]

>At the risk of repeating myself, my argument against Condorcet can be 
>summarised as follows:
>
>I do not support Condorcet because I believe that in practice, regardless 
>of the theoretical and conceptual advantages it may possess, it would be 
>too favourable towards parties who succeed in positioning themselves in 
>the centre and correspondingly discriminatory against wing parties.

Too favorable is, of course, a matter of opinion.  There's something 
undeniably meaningful about saying a candidate would beat any other 
candidate if they were the only two running.

>IRV succeeds, I believe, in striking a balance between the two somewhat 
>conflicting aims of ensuring that a candidate has majority support ( a 
>candidate does not win with a minority of the vote because the opposition 
>is split)

IRV does nothing of the sort.  It simply fails to hand the election to a 
candidate with the largest core of support in different cases than 
Condorcet.  Consider this scenario:

10% FarRight>Right>Centrist>Left>FarLeft
10% Right>FarRight>Centrist>Left>FarLeft
15% Right>Centrist>FarRight>Left>FarLeft
16% Centrist>Right>Left>FarRight>FarLeft
15% Centrist>Left>Right>FarLeft>FarRight
13% Left>Centrist>FarLeft>Right>FarRight
11% Left>FarLeft>Centrist>Right>FarRight
10% FarLeft>Left>Centrist>Right>FarRight

Centrist wins the election in every deterministic voting scheme known to 
man, except IRV.

>I would probably counter it with my favourite 49 A>B>C, 3 B>A>C, 48 C>B>A 
>example with some comment about the importance of first preference 
>votes/utility, somebody else would them make a comment about how first 
>preference votes have no significance of themselves and so it goes on .........

In this scenario, 97% of the voters prefer someone other than B.  In order 
to win the election, B has to convince 96% of the 97% (i.e. about 99% of 
the voters who don't fully support him) to back him with their second place 
votes.  If the candidate can actually manage that, then he's not some 
weasely "weak centrist"; he's a real compromise and has convinced the 
electorate of this.  The only way you'd ever see an election like this 
would be if A,B,and C were all well known, and were all extremely close in 
viewpoint, yet still managing to be clearly distinct with A and C slightly 
more extreme.

Of course, B doesn't have to convince quite as many people to put him on 
their ballot if he has more fist place support.  But then he stops looking 
so weak, doesn't he?

>To get a reasonable result from Approval voting the voter needs to have at 
>least a working knowledge of how to vote strategically in an Approval 
>election. This is my major objection to Approval. I feel that that many, 
>if not a majority of voters when presented with the Approval question will 
>take the question at face value and vote for all the candidates they 
>approve of. Very few people unfamiliar with AV strategy will look at the 
>instruction and think " ah, what I need to do is approve every candidate 
>whose utility ( to me ) exceeds that of the candidate most likely to win" 
>or any similar thing. If people do use strategy it is more likely to be on 
>the level of " well I approve of A,B and C, oh but if I approve all of 
>them I'll have approved 3 of the 4 candidates on the ballot, maybe that's 
>too many. Well, I like A and B a lot more than C so I'll only approve A and B".

A few responses:

1)  People aren't idiots so they will probably only approve one of the 
front-runners in a race.  Understanding this isn't any harder than 
understanding the LO2E problem, which most people are capable of.

2)  Parties will tell their supporters how to vote.

3)  There are lots of potential strategies, but only the most hairbrained 
will actually produce bad results with any consistency.  People can mix the 
"above average utility" and the "favorite frontrunner plus" and the "above 
frontrunner, plus frontrunner maybe" and the "above average expectation" 
and the "just like I would vote in plurality" strategies to their heart's 
content, and the final results will probably turn out fine.


>Getting back to one of James Green-Armytage's points I feel that IRV 
>supporters attacking Approval supporters attacking Condorcet supporters in 
>public ( as opposed to an internet discussion group like this) is the 
>surest way on this Earth to maintain plurality.

If there was an IRV movement in my area, I'd do my darndest to argue 
against them semi-privately (i.e. not at a city council meeting, hopefully) 
and turn them to Condorcet.  Most IRV supporters simply aren't aware of 
IRV's flaws, after all.  But if IRV were on the ballot, I'd vote for it.
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