[EM] Why does IRV but not delayed top-two runoff lead to 2-partydomination?

[Jan Kok]

On 2/24/07, Michael Ossipoff <mikeo2106 at msn.com> wrote:
>
> Jan Kok wrote:
>
> >The statistical evidence at http://rangevoting.org/TTRvIRVstats.html
> >seems pretty good that IRV leads to two party domination in IRV
> >elections, while (delayed) top two runoff tends to lead to a strong
> >multiparty system.
> >
> >Why do those two methods, which seem strategically quite similar, lead
> >to such different results?
>
> In 2-balloting top-2 Runoff, the CW can't lose if s/he comes in 1st or 2nd
> in the first balloting.

Ok. How does that lead away from 2 party domination? Can you show a
scenario where voter incentives are different for IRV and TTR?

>
> You said:
>
> >Most IRV supporters in the US have no clue that voting their favorite
> >1st can ever hurt them. From my limited discussions with Australians,
> >it seems most of them have no idea either.
>
> I reply:
>
> My discussions with Australians suggests the opposite. They told me that
> it's difficult for small parties to get 1st place votes, because voters
> don't want to waste their vote. Voters want to vote one of the big-2
> parties' candidates in 1st place, for strategic reasons. Do they know
> something about IRV that American IRVists don't know? :-)
>
> One Australian I spoke with even told me that she herself had insincerely
> voted a top-2 candidate iln 1st place, insincerely downranking her favorite.

Are there any Australian web sites, blogs, newspaper or magazine
editorials, etc. that criticize IRV?

http://australianpolitics.com/voting/systems/preferential.shtml is not
strongly critical but does say "It [IRV] promotes a two-party system
to the detriment of minor parties and independents." I've asked the
author of that site why he said that, but haven't received a response.

Cheers,
- Jan