[EM] Scenario where IRV and Asset outperform Condorcet, Range, Bucklin, Approval.

[C.Benham]

Kristofer,

>Is it possible to make a two-candidate runoff at all so that the runoff 
>passes mono-raise if the voters vote exactly as before? 
>

The top two in the Ranked Pairs order should fill that bill for what its 
worth.

>>/ A better 2-round scheme would be to have all the members of the Smith set eligible
>/>/ for the second round, which uses simple Approval.
>/
>Smaller sets might be better, but I'm not sure which are resistant 
>against the strategy Jameson shows. Uncovered set? Dutta set? etc...
>  
>

I forget what the Dutta set is. With the the Uncovered set, there may be 
a theoretical mono-raise problem.


>One problem with Approval is that voters then have to have accurate poll 
>data in order to run things like "frontrunner plus" or "LeGrand strategy 
>A". Would this be less of a concern if the Approval is limited to the 
>Smith set (or a smaller set contained in it), as it would for your 
>runoff method?
>

I envisage that the voters would have the pairwise (and presumably also 
the first-preferences) results from the
first round to guide their strategising.

One possibility is to use some algorithm that combines information from 
both rounds, not necessarily simply electing
the second-round winner.


Chris Benham



Kristofer Munsterhjelm wrote (13 May 2010):

Chris Benham wrote:
>/ 
/>/ Kristofer Munsterhjelm wrote (12 May 2010):
/>/ "One idea of mine, although extremely complex, would be to select the two 
/>/ candidates for a runoff by two Condorcet methods - one that's resistant 
/>/ to strategy (like Smith,IRV), and one that's not but provides better 
/>/ results in the honest vote case (e.g. Schulze, uncovered methods). Since 
/>/ the second round is honest - a two-candidate election where a majority 
/>/ wins is strategy-proof - it should lower the chances of ending up with a 
/>/ very bad candidate.
/>/ 
/>/ If the two methods agree, the candidate would win outright."
/>/ These sorts of schemes (a runoff between the winners of methods A and B)
/>/ invariably fail mono-raise and are vulnerable to Pushover strategy.
/
Is it possible to make a two-candidate runoff at all so that the runoff 
passes mono-raise if the voters vote exactly as before? Would a runoff 
between the winner and second-place finisher in Schulze work? I suppose, 
but then one would lose the strategy resistance...

>/ "The voters may also end up arguing that because the two methods agree so often 
/>/ (if they do), there's no need to have the runoff in the first place; if the method 
/>/ deters organized strategy, the organized strategy wouldn't appear and so the actual 
/>/ runoff mechanism would appear superfluous."
/>/  
/>/  
/>/ So "the threat of a runoff (that is never needed to be held) is deterring organised
/>/ strategy" is somehow an argument for abolishing the threat??
/
No, but voters may think so. I'm particularly thinking of cases where 
IRV/STV "seemed to give the same result as Plurality after a lot of 
counting" and so was abolished, which of course then degraded the 
results in the cases where they didn't agree.

>/ A better 2-round scheme would be to have all the members of the Smith set eligible
/>/ for the second round, which uses simple Approval.
/
Smaller sets might be better, but I'm not sure which are resistant 
against the strategy Jameson shows. Uncovered set? Dutta set? etc...

One problem with Approval is that voters then have to have accurate poll 
data in order to run things like "frontrunner plus" or "LeGrand strategy 
A". Would this be less of a concern if the Approval is limited to the 
Smith set (or a smaller set contained in it), as it would for your 
runoff method?


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