[EM] Instant 2-stage plurality/pairwise runoff

atarr at purdue.edu atarr at purdue.edu
Tue Mar 12 08:31:52 PST 2002

Steve Wrote,

> I am interested in the fact that the traditional 2 stage plurality 
> runoff will always choose a Condorcet Candidate, when one exists, 
> if that candidate is among the top 2 plurality candidates in the 
> first round. This suggests that we should consider an instant 2-stage 
> runoff procedure where preference ballots are used, and the top two 
> plurality candidates go into an instant pairwise vote.

It does not suggest this.  The key problem is that one caveat you mention, "if 
that candidate is among the top 2 plurality candidates in the first round."  We 
have no guarantee that this will be the case, and indeed it will not be the case 
in many scenarios.  In particular, the classic (on this list anyway) "left 
middle/right" scenario can cause middle, the obvious Condorcet winner, to finish 
last in the first round of plurality.  Demorep likes to use the stark Stalin 
Wahington/Hitler example to illustrate this.

As an interesting side note, the nation of Sri Lanka (just south of India) 
recently switched over to such an instant two stage runoff (we called it ITTR in 
a thread a few months ago, for instant top two runoff).  Thus far, their ITTR 
elections have produced the same results that a plurality election would have.  
It should be interesting to watch.  ITTR is better than IRV, although both are 
pretty bad. 


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