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

[Dave Ketchum]

IRV completes its election on election day.  We know the winner.  While we 
could and should know who was second, there is nothing to be done about 
such.  Voters do not have solid data as to other candidates.

TTR:
      Can complete election in one day - but, even here, we should know 
who was second and how much they lagged.
      With runoff we hear more from second - helps remind, especially when 
second is from a third party.

Condorcet completes on election day, but we have more data about all the 
candidates to discuss:
      Easy to identify and discard the dregs.
      Can compare third parties with each other and with their histories - 
which are, or are likely to become, threats to the major parties.
      Thus voters can see their effects on data, and be encouraged to 
campaign and vote to increase that.

DWK

On Fri, 23 Feb 2007 04:17:02 -0700 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? The above mentioned page has links to some
> speculations/explanations, which I find less than convincing. The main
> proposed reasons are:
> 
> 1. Different strategy calculations by voters under the two systems.
> Voters who like a "third party" candidate seem more willing to vote
> for their favorite in the first round of TTR, than corresponding
> voters under IRV are willing to rank their favorite 1st. Why, why?!?
> 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. So why aren't Australians
> voting for third party candidates as their first choices, enough that
> they might occasionally win? While at the same time, voters in TTR
> countries feel free to vote for whoever they want, often enough that
> TTR countries tend to have flourishing multiparty systems?
> 
> 2. Under IRV, if a "third party" candidate makes it to the last round,
> it draws little attention from the media. But under TTR, when there is
> a runoff, both candidates get equal attention for several weeks. This
> lets the finalists compete on an equal basis, so the third party has a
> realistic chance to win, and even if hse does not win, the party and
> candidate will be remembered in the next election.
> 
> So, is either or both of those the real explanation(s)? Is there some
> evidence to back up these explanations? (I suppose statements by
> Australians, Irish, etc. saying that third party candidates rarely get
> any attention from the press, and statements by Argentinians, etc.
> that third party candidates _do_ get a lot of attention from the
> press, would be helpful.)
> 
> It would be nice to put together some convincing and preferably
> non-technical explanation about why IRV leads to two-party domination
> and TTR does not. The purpose is to persuade IRV supporters to leave
> US TTR elections alone, or convert to something better than IRV.
> 
> Thanks,
> - Jan

-- 
  davek at clarityconnect.com    people.clarityconnect.com/webpages3/davek
  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
            Do to no one what you would not want done to you.
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