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

[Markus Schulze]

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.

******

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. On the other side, when IRV is used then clones cannot
influence who gets to the final round.

******

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

Markus Schulze