[EM] Strategic Voting and Simulating It

[Kevin Venzke]

Hi Raph,

--- En date de : Jeu 16.10.08, Raph Frank <raphfrk at gmail.com> a écrit :
> De: Raph Frank <raphfrk at gmail.com>
> Objet: Re: [EM] Strategic Voting and Simulating It
> À: stepjak at yahoo.fr
> Cc: election-methods at electorama.com
> Date: Jeudi 16 Octobre 2008, 4h55
> On Thu, Oct 16, 2008 at 2:23 AM, Kevin Venzke
> <stepjak at yahoo.fr> wrote:
> > Each voter's sincere utilities are determined
> randomly and independently,
> > which is problematic because it does not produce
> realistic scenarios. It
> > would be better to combine voters into factions,
> although it would be no
> > easier to reach consensus regarding what simulation is
> realistic.
> 
> I think Warren has some simulations where the voters are
> spread over
> 1-2 axes.  (He can comment).  My understanding is that
> there are lots
> of different distributions.

Ok. That is better. But you still have the problem that it's open to
endless debate, what exactly the realistic simulation method is.

> > Two frontrunner candidates are determined essentially
> at random, and this
> > information will be used by the strategic voters. This
> is problematic
> > because usually when a candidate is called a
> "frontrunner" this means
> > there is a perception that this candidate is likely to
> win, before any
> > strategy is used. When the frontrunners are determined
> randomly, this is
> > not realistic unless you hold a very pessimistic view
> about how a
> > candidate becomes a "frontrunner" in real
> life.
> 
> In plurality, it is self reinforcing.  The top-2 are front
> runners
> because they are supported by the party, and thus are
> likely to win.
> 
> Party support makes them likely front runners and that then
> makes them
> actual front runners.

But this ignores the fact that parties still want to try to win the
election. If they back candidates at random, they could conceivably hold
on to frontrunner positions, but they wouldn't generally win, so they 
don't do this.

> In such a situation, random doesn't seem entirely
> unrealistic,
> electing 2 candidates via honest PR-STV might better
> simulate the
> primary system.

It is still a problem to take this interpretation of FPP as a starting
principle to measure *all* rank ballot methods.

> > The strategic voters, in any rank ballot method, will
> simultaneously use
> > favorite betrayal compromise strategy and also burial
> strategy. There is
> > no calculation, or awareness of the specific election
> rule. The strategic
> > voters seem schizophrenic in that they are
> sufficiently paranoid about
> > losing their compromise choice that they will abandon
> any actually
> > preferred candidate, but at the same time they are
> sufficiently reckless
> > that they will rank the worse "frontrunner"
> dead last even though in
> > methods where this can be an effective strategy, it
> also creates a major
> > risk that the winner will be a candidate that nobody
> likes.
> 
> It is a problem that strategy has to be based on
> assumptions of the
> simulator.  However, maybe my suggestion in the other
> thread would
> help.

I am not sure I've seen the other thread but I'll look for it.

> > Nomination (dis)incentives can't be examined
> either.
> 
> True.  It might be possible to test nomination strategy
> directly.  For
> example, the 2nd place candidate might be cloned with a
> slight offset
> in utilities and the election ran again.

Perhaps... I've never written a simulation to study nomination incentive
specifically, but I have written e.g. a FPP simulation, in which
voters stop voting for a candidate (in the polls leading up to the
election) when the calculated benefit to the vote disappears. And in
FPP there is no way for the benefit to come back (in contrast to, say,
Approval, which in my simulations of the same sort had the potential to
never arrive at stability).

Kevin Venzke