[EM] Why I Prefer IRV to Condorcet

[Juho Laatu]

Yes, it is not intuitive to abandon one's favourite. What is then intuitive? Burying as a Condorcet strategy is certainly not intuitive (quite difficult to understand even to experts). Burying in the sense of ranking the strongest competitor of one's favourite potential winner last may be intuitive to many.

Since in Condorcet there are some situations where burying is a working strategy, this property (if advertised) may encourage people to (irrationally) bury (or rank the competitors last) even more generally. In IRV voters may also intuitively bury although that doesn't make much sense.

In Condorcet one would thus have to trust "political advisers" to tell when to bury (to make the strategy rational). Similarly in the example that I gave the voters would maybe have to be reminded that it could be wise to compromise this time.



Although all the three factions are large the B supporters may see C as a spoiler. If C would not participate both B and C supporters would be happier with the outcome. (C thus spoils the result also from the C supporters' point of view.)

In the example B and C could be candidates of the same party. Then nominating also C (the more extreme of the two potential candidates) was maybe a mistake.

Juho



--- On Sat, 22/11/08, Greg <greg at somervilleirv.org> wrote:

> From: Greg <greg at somervilleirv.org>
> Subject: Re: [EM] Why I Prefer IRV to Condorcet
> To: juho4880 at yahoo.co.uk
> Cc: election-methods at lists.electorama.com
> Date: Saturday, 22 November, 2008, 10:04 AM
> Yes, this is as intuitive as it comes in terms of IRV
> strategy, but I
> still find it ultimately counter-intuitive for the average
> voter.
> Candidate C has a the second-most number of first choices,
> which
> likely corresponds to the second-biggest campaign
> (second-most amount
> of money, volunteers, name recognition, exposure, ads,
> etc). The
> thought of abandoning C in favor of B, who will probably
> have a
> smaller campaign (less money, fewer volunteers, etc), I
> think will
> strike the average voter as counter-intuitive. In these
> respects, this
> scenario is quite unlike the standard spoiler scenario,
> where the
> incentive is to intuitively switch one's vote from the
> smaller to the
> bigger campaign. Nevertheless, I would agree that it's
> something to be
> on the lookout for as IRV spreads.
> 
> Greg
> 
> 
> On Sat, Nov 22, 2008 at 2:00 AM, Juho Laatu
> <juho4880 at yahoo.co.uk> wrote:
> > Here's one IRV example with three strong
> candidates and where voters do have some incentive to
> compromise.
> >
> > 45: A>B>C
> > 10: B>A>C
> > 15: B>C>A
> > 30: C>B>A
> >
> > We have one centrist candidate (B) between two others.
> >
> > According to this poll it seems that B will be
> eliminated first, and then A would win since some B
> supporters prefer A to C.
> >
> > If sufficient number of C supporters would abandon
> their favourite and vote B>C>A, then C would be
> eliminated first and the centrist candidate B would be
> elected.
> >
> > Based on this poll it seems that if C voters don't
> compromise (or if C will not withdraw) then from C
> supporters' point of view the worst candidate (A) will
> be elected.
> >
> > - This situation could be reasonably common (or
> plausible) in real life
> > - B is a Condorcet winner ((that IRV would not elect))
> > - B seems to be politically closer to C than to A
> > - C is not a weak candidate since with few more
> "core" voters or second place support it could
> beat A (if the strong centrist candidate B will be
> eliminated first)
> >
> > C supporters could be optimistic and hope for a change
> in opinions before the election day. I mean that in real
> elections many voters may be optimistic and fighting
> spirited and believe rather in those earlier polls that gave
> their favourite more votes than this poll etc.
> >
> > The strategy of the C voters is not very
> "intuitive" in the sense that it is never natural
> to abandon one's favourite (it could be easier e.g. to
> rank the strongest competitor last even if that would be an
> irrational strategy). But on the other hand it is quite
> straight forward to see from the poll results (maybe voiced
> out by media) that indeed it makes sense for the C
> supporters to give up and abandon C if people will vote as
> indicated in this poll. The voters will thus have a dilemma,
> whether to vote sincerely or whether to compromise.
> >
> > Juho
> >
> >
> >
> > --- On Sat, 22/11/08, Greg
> <greg at somervilleirv.org> wrote:
> >
> >> From: Greg <greg at somervilleirv.org>
> >> Subject: Re: [EM] Why I Prefer IRV to Condorcet
> >> To: election-methods at lists.electorama.com
> >> Date: Saturday, 22 November, 2008, 3:06 AM
> >> Thanks, Chris. I'll correct the errors and
> rephrase some
> >> things I
> >> didn't say correctly.
> >>
> >> On the Compromise strategy, I think some
> compromises are
> >> more
> >> intuitive than others. I think it's intuitive
> to
> >> abandon a more weakly
> >> supported candidate, e.g. Nader, in favor of a
> major
> >> candidate, as is
> >> common in FPTP. But it strikes me as more
> >> counter-intuitive, at least
> >> for the average voter, to abandon a candidate with
> strong
> >> core support
> >> in favor of a more weakly supported candidate, as
> could
> >> happen under
> >> IRV. Then there's the issue as to whether the
> result of
> >> the
> >> strategizing is a better or worse result overall .
> . . but
> >> that's a
> >> tricky topic for another time.
> >>
> >>
> >> > Date: Thu, 20 Nov 2008 11:51:01 -0800 (PST)
> >> > From: Chris Benham
> <cbenhamau at yahoo.com.au>
> >> > Subject: [EM]  Why I Prefer IRV to Condorcet
> >> >
> >> > Greg,
> >> > I generally liked your essay. I rate IRV as
> the best
> >> of the single-winner methods that
> >> > meet Later-no-Harm, and a good method (and a
> vast
> >> improvement on FPP).
> >> >
> >> > But I think you made a couple of technical
> errors.
> >> >
> >> > "However, because bullet voting can help
> and
> >> never backfire against one's top choice under
> >> > Condorcet, expect every campaign with a shot
> at
> >> winning to encourage its supporters to
> >> > bullet vote. "
> >> >
> >> > Bullet voting can "backfire against
> one's top
> >> choice under Condorcet" because Condorcet
> >> > methods, unlike IRV, fail Later-no-Help.
> >> >
> >> >
> >>
> http://groups.yahoo.com/group/election-methods-list/files/wood1996.pdf
> >> >
> >> > In this 1996 Douglas Woodall paper, see
> "Election
> >> 6" and the accompanying discussion on
> >> > page 5/6 of the pdf (labelled on the paper as
> >> "Page 13").
> >> >
> >> > Quoting again from your paper:
> >> > "As mentioned, every voting system is
> >> theoretically vulnerable to strategic
> manipulation, and IRV
> >> > is no exception. However, under IRV, there is
> no
> >> strategy that can increase the likelihood of
> >> > electing one's first choice beyond the
> opportunity
> >> offered by honest rankings. While there are
> >> > strategies for increasing the chances of less
> >> preferred candidates under IRV, like push-over,
> >> > they are counter-intuitive."
> >> >
> >> > The Push-over strategy is certainly not
> limited to
> >> improving the chance of electing a "lower
> >> > [than first] choice". Say sincere is:
> >> >
> >> > 49: A?
> >> > 27: B>A
> >> > 24: C>B
> >> >
> >> > B is the IRV winner, but if? 4-21 (inclusive)
> of the A
> >> voters change to C or C>? then the winner
> >> > changes to A.
> >> >
> >> > But as you say the strategy isn't
> >> "intuitive" , and backfires if too many
> of the A
> >> supporters try it.
> >> > Some IRV opponents claim to like Top-Two
> Runoff, but
> >> that is more vulnerable to Push-over
> >> > than IRV (because the strategists can support
> their
> >> sincere favourite in the second round).
> >> >
> >> > The quite intuitive strategy that IRV is
> vulnerable to
> >> is Compromise, like any other method that
> >> > meets Majority. But voters' incentive to
> >> compromise (vote one's front-runner
> lesser-evil in first
> >> > place to reduce the chance of front-runner
> >> greater-evil winning) is generally vastly vastly
> less
> >> > than it is under FPP.
> >> >
> >> > (There are methods that meet both Majority
> and
> >> Favourite Betrayal, and in them compromisers
> >> > can harmlessly vote their sincere favourites
> in
> >> equal-first place.)
> >> >
> >> > But some Condorcet advocates are galled? by
> the
> >> Compromise incentive that can exist where
> >> > there is a sincere CW who is not also a
> sincere Mutual
> >> Dominant Third winner.
> >> >
> >> > 49: A>B
> >> > 02: B>A
> >> > 22: B
> >> > 27: C>B
> >> >
> >> > On these votes B is the CW, but IRV elects
> A.? If the
> >> C>B voters change to B then B will be
> >> > the voted majority favourite, so of course
> IRV like
> >> Condorcet methods and FPP will elect B.
> >> >
> >> > Chris Benham
> >> ----
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> >> http://electorama.com/em for list info
> >
> >
> >
> >
> >