[EM] Top Two Runoff versus Instant Top To Runoff

[Juho Laatu]

Kristofer Munsterhjelm wrote:

> Say that the runoff method is "pick first and second
> place winners of the base method". Then any strategy
> that boosts your preferred candidate to either first or
> second place can be used

One could also promote a candidate that is likely to
lose to one's favourite at the second round. Here's one
example.

(To fsimmons) In this example TTR is also less Condorcet
efficient (in addition to being more manipulable).

Sincere opinions:
45: A>B>C
15: B>A>C
15: B>C>A
25: C>B>A

In both TTR and IRV (with sincere voting) the second
round would be between A and B. B would win.

If 10 of the 45 A supporters would vote for C at the
first round in TTR, then the second round would be
between A and C, and A would win. But in IRV the
strategic A supporters would be bound to vote for C
at the second round, and C would win.

(If too many A voters vote for C at the first round,
then the second round will be between B and C. But
this is still safe to from the A supporters' point
of view (if the polls are accurate) since also
without the strategy B would win.)

> "just to show them"

Yes, the reactions of people to strategies are
important. One should check also these factors
systematically when estimating the feasibility
of different strategies in real life.

There may be societies where those that do not
use strategies are considered fools, but there
are also societies where trying to cheat to win
is seen as a very bad thing.

Strategic attempts may backfire already at the
first round. In large public elections strategies
that require coordination or marketing can not be
hidden.


Some further (rather wild) speculation:
- One could arrange elections with as many rounds
as needed (maybe without elimination)
- Maybe this is more valid for electorates or
permanent bodies like parliamnets than for large
public elections (unless electrical and PC/mobile
based)
- One approach is to change the candidate proposals
as needed after each round to help reaching consensus
- One could e.g. elect both the prime minister,
government coalition and political program at the
same time (each proposal would consist of a
combination of such components)
- One could use Condorcet and vote until a Codorcet
winner is found
- Parties and politicians would modify their
proposals until a good enough proposal is found
- Maybe there would be some special rule to
termoinate the process if it gets too long
- One possibility would be to start reducing the >50%
limit (to win all other proposals) after say 10 rounds

Juho



--- On Sun, 23/11/08, Kristofer Munsterhjelm <km-elmet at broadpark.no> wrote:

> From: Kristofer Munsterhjelm <km-elmet at broadpark.no>
> Subject: Re: [EM] Top Two Runoff versus Instant Top To Runoff
> To: fsimmons at pcc.edu
> Cc: election-methods at lists.electorama.com
> Date: Sunday, 23 November, 2008, 6:11 PM
> fsimmons at pcc.edu wrote:
> > 
> >  Kevin,
> >  I know that you have studied Top Two Runoff more
> deeply than I have.  Here in Oregon measure 65 was defeated
> recently.  It was a version of top two runoff in which the
> the first round of the runoff replaced the traditional
> primaries, i.e. it was cast as one grand open primary for
> all parties and all voters, from which the top two vote
> getters advance to the other stage in November.
> >  It was interesting that the IRV organization FairVote
> was against the measure, even though there was no IRV
> initiative on the ballot.
> >  It seems to me that Top Two Runoff might be more
> manipulable than the instant version of the same, since
> voters could vote insincerely in the first round without
> having to worry about that messing up their choice in the
> other stage.
> >  I would be interested in your thoughts on this
> matter.
> 
> I'm not Kevin, but I think I can comment. In any method
> that's [some base method] + runoff, where the runoff
> candidates are picked from the social ordering of the base
> method, the existence of the second round would increase the
> incentive to strategize.
> 
> However, it would not make it safe to always strategize.
> Say that the runoff method is "pick first and second
> place winners of the base method". Then any strategy
> that boosts your preferred candidate to either first or
> second place can be used - but if the strategy, when applied
> too greedily, causes both first and second place to be
> replaced by candidates you don't like, there's an
> incentive to be careful.
> 
> That's weaker than it is for just applying the base
> method and picking the winner. If you use strategy in the
> base method case, and you displace your true winner in favor
> of someone that you really loathe, then you're out of
> luck. For that to deter you from using strategy in a runoff,
> it has to displace both the candidates that would get into
> the runoffs.
> 
> One should also be aware that the second round, taken as a
> separate election, will be honest. That's because there
> are only two candidates and a simple majority election is
> strategyproof in that case. So that may weight against the
> increased incentive to use strategy in the first round.
> Whether this makes the method (in general) more fragile
> (attracting more strategy) or more robust depends on which
> component is stronger: the incentive to strategy in the
> first round, or to honesty in the second. That probably
> depends on the base method.
> 
> There may also be inter-round strategy. Say that there are
> two wings and a center. In the first round, the left wing
> runs a strategy. It's discovered. Now, the centrists may
> support the right-wing candidate in the second round
> "just to show them", whereas they wouldn't
> otherwise. To the degree that runoffs are two elections,
> such effects may occur.
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