[EM] Consensus?: IRV vs. Primary w/Runoff

[Forest Simmons]

On Fri, 1 Feb 2002, Markus Schulze wrote:

> Dear Forest,
> 
> you wrote (1 Feb 2002):
> > But (as I argued in a previous posting) the CW is less likely to survive
> > the tortuous path to the final round in IRV, especially considering all of
> > the propaganda telling voters that they can vote their sincere preference
> > order and still end up with "The Majority Choice."
> > The fallacy of that propaganda is more apparent in the simpler method, so
> > the voters are more likely to vote seriously in the primary, and (almost
> > surely) get the CW into the finals (if there is a CW).
> 
> If the Condorcet winner isn't the favorite candidate of the largest or the
> second largest group of voters then it doesn't help him very much when the
> voters vote "seriously" in the primary.

What you say is true if the two largest groups like each other's
candidates or in a zero information election.  Otherwise, they are apt to
abandon favorite for CW unless they are sure of winning in the finals. 

I don't claim that Runoff will always pick the CW, only more often than
IRV.


> 
> ******
> 
> You wrote (1 Feb 2002):
> > It seems to me that Primary with Runoff is virtually independent from
> > clones, too, because it would take at least a two thirds majority to get
> > two clones as finalists, unless the voters are asleep.
> 
> When primary with runoff is used then a party doesn't need a two thirds
> majority to manipulate the result of the elections by running clones.
> It is only necessary that the clones take so many votes away from the CW
> that he falls behind the candidate with the third largest number of first
> preferences.

How can they do this if they have less than two thirds of voters on their
side?

If more than one third of the voters don't want two clone candidates to
survive to the finals, they can agree to vote for the CW or some other
candidate that they prefer and prevent one of the clones from surviving to
the finals.
 


> ******
> 
> You wrote (1 Feb 2002):
> > It (the instant version of Primary with Runoff) is summable, has simpler
> > strategy, is less likely to eliminate the sincere CW, and (I believe) is
> > less manipulable.
> 
> It is questionable whether summability is desirable. E.g. Nurmi
> and Bartholdi consider summable methods to be more manipulable.

They have a strange conception of manipulability.

> And your argument that primary with runoff "has simpler strategy"
> is rather an argument against primary with runoff.

In what way?

Forest