[EM] Philosophical question for IRV experts

[Kevin Venzke]

Paul,

 --- Paul Kislanko <kislanko at airmail.net> a écrit : 
> The situation is a truncated ballot one: the task is to pick the top 25
> teams from a field of 117, so no one can vote for more than 25. I realize
> that a better approach to this would be full ranked ballots and some form of
> PR-STV, 

If you just want a ranking of the best teams, you probably don't want to 
use a PR method anyway, since that will try to represent the voters 
proportionally.

> But here's my question. The process I used to assign a team (candidate) to
> rank x was "team A has the greatest majority of votes for rank x or higher
> than any team ranked below x-1". In some cases there are multiple teams with
> a majority at ranking x, so I select the largest majority for position x and
> proceed to calculating the rankings for position x+1.
>  
> Now, if teams B and C were second and third for position x and both had
> majorities, but when they lose position x and we add in the votes for x+1,
> they are third and second, respectively, did I make a mistake by not
> assiging ranks x+1 and x+2 at the x step?
>  
> In the attachment, a relevant example is the relative position of #11 and
> #12. In the battle for #10, Miami was ahead of LSU, but once the votes for
> 11th place were added in, LSU was ahead.
>  
> In this context it would seem more correct than what I did to "fix" a
> ranking whenever the team receives a majority, so I could've assigned 10th,
> 11th and 12th positions all in step 10. Or not?
>  
> Which approach is right?

The only non-PR way I can think to do IRV to obtain a ranking of the
candidates is to
1. find the IRV winner
2. delete him from all the ballots as though he hadn't been an option
3. repeat.

This seems like too much work to me, so I wouldn't suggest using IRV for
this.

The method you describe is interesting, though. In the single-winner
case, it seems equivalent to Plurality.

Kevin Venzke



	

	
		
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