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

[Forest Simmons]

On Fri, 1 Feb 2002, Markus Schulze wrote:

> Dear Forest,
> 
> you wrote (31 Jan 2002):
> > The more manipulable a method is, the easier it eliminates the
> > sincere Condorcet Winner. A method that places a premium on
> > first place preferences and still eliminates the CW, even when
> > the CW has the greatest first place preference, is a very
> > manipulable method. That's IRV. As Mike noted, primary with
> > runoff will not eliminate the CW if it has the greatest number
> > of first place preferences.  Even if the CW comes in second
> > place in number of first preferences, it will still win.
> > That's a pretty good indicator of the relative manipulability
> > of the two methods.
> 
> That's hardly an argument. Also IRV chooses the Condorcet
> winner whenever he gets to the final round. 

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).

> I rather consider
> IRV to be less manipulable than primary with runoff because
> IRV is independent from clones.

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. 

If a party has a two thirds majority, then they could argue that they have
the right to decide who the two finalists are. 

> Which important criterion
> does primary with runoff meet that is not met by IRV?

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.

I don't want to spend too much time arguing that IRV is no better than
Primary with Runoff.  But I think it may help dispel some of of IRV's
mystique, or in other words, let some of the hot air out of the bag.

Forest