[EM] IRV in action

Adam Tarr atarr at purdue.edu
Wed Apr 2 10:26:09 PST 2003

James Gilmour wrote:

>But the thinking behind the use of the word in this context is also 
>You have to remember that IRV is nothing more than a convenient method of
>condensing an exhaustive ballot into one voting operation.  (It also 
>avoids all
>the horse-trading that typically takes place between the successive rounds 
>of an
>exhaustive ballot, but that's a different issue.)

Some have argued that this "horse trading" allows compromise candidates to 
stave off defeat.

>See my comment above.  Whatever other defects it may have, IRV does ensure 
>the winner has the support of half or more of those who are voting at the 
>when the final decision is made.

The winner does have "the support of half or more of those who are voting", 
but only over the remaining candidates.  You can't overstate the 
significance of that.  Good candidates, candidates who have more support by 
any reasonable measure, can be discarded by IRV before a final decision is 
made.  Here's just such a "nightmare" example:

10% FarRight>Right>Centrist>Left>FarLeft
10% Right>FarRight>Centrist>Left>FarLeft
15% Right>Centrist>FarRight>Left>FarLeft
16% Centrist>Right>Left>FarRight>FarLeft
15% Centrist>Left>Right>FarLeft>FarRight
13% Left>Centrist>FarLeft>Right>FarRight
11% Left>FarLeft>Centrist>Right>FarRight
10% FarLeft>Left>Centrist>Right>FarRight

"Centrist" has the most first place votes, the most second place votes, and 
the most third place votes.  Also, centrist is never ranked fourth or fifth 
on any ballot.  In any non-probabalistic election method except for IRV, 
centrist wins in a landslide.  But in IRV, centrist is eliminated in the 
third runoff, and Right beats left 51-49.

The results won't usually be that blatantly undemocratic, of course, but 
the fact remains that the best candidate by most reasonable measures can be 
eliminated early in an IRV election.  Claiming that the winner has majority 
support, without adding the caveat that that support only applies vis-a-vis 
the remaining candidates, deems like a distortion of the truth to me.


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