[EM] Smith//MMPO

C.Benham cbenham at adam.com.au
Thu Sep 29 11:48:50 PDT 2016


The example we are discussing:

30: A  (sincere may be A>B)
20: B>A
25: C>B

You like that Winning Votes and Smith//MMPO  elects B.

On 9/29/2016 12:49 AM, Michael Ossipoff wrote:

> Voters will do what it takes, to elect a candidate whom they perceive 
> as the CWs (sincere CW).

C:   How do you know that?   Won't they  (at least also) try to elect 
candidates they prefer to their perceived "sincere CW"?
If you are right, then presumably in our example the 3 factions of 
voters all have different "perceived sincere CWs" because
they voted for different candidates.

> Natural, non-strategic, top-cycles are vanishingly rare in political 
> polls. At CIVS (Condorcet Internet Voting Service) I'm not aware of 
> there ever having been a top-cycle for top-finisher.
> So. Most likely there _is_ a CWs (sincere CW).

C: That isn't rational. Presumably a  ballot set like our example, with 
30 A or 30 A>C  is also vanishingly rare. The question isn't how rare 
top-cycles in general are.
The question is how reasonable is to assume that the A truncators in 
this particular example are insincere.

In essence an election method should aim to achieve just two things: 
maximise probable Social Utility and minimise possible voter regret.  
If  fulfilling those aims
is done without electing some candidate that someone imagines is the 
"sincere CW", then that isn't a problem.

In the example there is no compelling rational reason to assume that any 
of the ballots are insincere.  So there is no "sincere CW".

A, as an uncovered positionally dominant candidate is presumably the 
highest SU candidate. (All the Condorcet methods I currently advocate 
would elect A).

So say we elect A.  In that case the 25 C>B voters might regret not 
making their second-choice win (in any Condorcet method) by voting C=B 
(or B>C or B).

But say instead  Winning Votes or  Smith//MMPO is used and we elect B.  
In that case the 30 A voters would regret not causing their favourite to 
win by
voting A>C.

And that clinches the case for any good method that elects A versus any 
method that elects B with the 30 A voters truncating, and A when they 
vote A>C.

Approval Sorted Margins isn't as bad because under it if the A 
supporters vote A>C it results in C winning. Also it meets 
mono-switch-plump and of course
(since above-bottom ranking is interpreted as approval) has some 
truncation incentive.

Chris  Benham

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