[EM] IRV vs Condorcet vs Range/Score

[Kristofer Munsterhjelm]

Raph Frank wrote:
> On 10/9/08, Dave Ketchum <davek at clarityconnect.com> wrote:
>>      If there is a near tie among three or more, they often disagree but
>> usually get one of the leaders - matters little since the leaders were about
>> equally deserving.
> 
> It matters because IRV reinforces the 2 party system.
> 
> it would be interesting to know what would be the effect of electing a
> parliament by condorcet voting from single seat districts.  It is
> possible that it would also result in a 2 party system.

Since Condorcet is a majoritarian method (as it needs to be in order to 
be a good single-winner method), the resulting parliament would also be 
majoritarian. This means that a party whose candidates consistently got 
low support in all districts would find none of those elected.

But Condorcet is also a better single-winner method than Plurality, so 
the candidates would be better representatives of the majority. They 
would probably be good compromise candidates, so the parliament would be 
less party-based than one elected by PR methods.

This might not be all that good for traditional parliaments; I don't 
know if the majoritarian nature would lessen competition (except in 
dominant-party states, where using Condorcet would be an improvement on 
Plurality in that respect), but it would reduce the voice of the minority.

It might be a good choice for an upper house decided to be a moderating 
counterweight to a populist lower house.

> However, based on certain assumptions, IRV is 2 party reinforcing.
> Also, Australia gives "experimental" evidence that IRV leads to a 2
> party system.
> 
> Condorcet wouldn't necessarily, so that is a good reason to at least try it.

It's possible that IRV is a bad single-winner method precisely because 
STV is a good PR method (with many seats). In STV, one doesn't need to 
find a candidate that covers a large area of opinion space, since other 
candidates can be used to cover those areas, but in IRV there are no 
other positions to be used in such a manner. I'm not sure if this is the 
reason, but it would fit well with my simulation results that 
"majoritarian IRV" (eliminate until only k remains for council size k) 
is a surprisingly good PR method, at least in absence of strategy.