[EM] Runoff vs IRV

[Dave Ketchum]

Around and around.

Seems like our proper position is that each of these are too crippled to 
deserve being adopted as new by any public election.

Which leaves promoting better understanding between Condorcet and these, 
and anything else with tolerable health.

Dave Ketchum

On Thu, 03 Jun 2004 04:56:51 +0000 MIKE OSSIPOFF wrote, and got some 
responses:

> 
> Though it would be hoped that we'd get something better than Runoff or 
> IRV, what if it were necessary to choose between those 2?
> 
> Of course they both have advantages compared to eachother, and examples 
> in which they do better than the other.
> 
> But what stands out, for me, is that Runoff always elects a CW who comes 
> in 1st or 2nd in the initial Plurality count, whereas IRV can fail to 
> elect a CW who is favorite to more people than anyone else is.
> 
> I've posted examples of that happening. I'll post them again here. They 
> aren't contrived or implausible examples. All it takes is for 
> favoriteness to taper away from the voter median position. That's a very 
> plausible scenario.
> 
> First I'll write this example in full, then I'll simplify it by leaving 
> out the preferences that IRV never looks at.
> 
> Example 1, complete:
> 
> 67: ABCDE
> 73: BACDE
> 100: CDBEA
> 84: DECBA
> 70: EDCBA
> 
> Example 1, simplified:
> 
> 67: AB
> 73: B
> 100: C
> 84: D
> 70: ED
> 
> It looks a bit sparse, doesn't it, after we delete the preferences that 
> IRV disregards.
> 
> When A & E get eliminated and transfer inward, C becomes the candidate 
> with fewest votes, though C is favorite to the most people. And of 
> course C is the CW too.
> 
> Example 2, simplified as before:
> 
> 49: AB
> 52: B
> 100: C
> 54: D
> 48: ED
> 
> This is an extreme example to show how badly IRV can fail in that way 
> with 5 candidates.  Example 1 is more typical. In Example 2, not only is 
> C the CW, and not only is C favorite to more voters than anyone else is, 
> as in Example 1, but this time C is favorite to about twice as many 
> people as anyone else is.
> 
> Now, as you said, IRV can save a CW who's Pliurality score is only 3rd 
> largest. But sometimes it won't. But the IRVers emphasize the importance 
> of favoriteness--that's their whole argument for IRV against Condorcet. 
> So then, how do they justify letting a big-favorite candidate (and CW) 
> lose, giving up Runoff's reliable protection for 1st or 2nd-placing CWs, 
> in order to maybe, sometimes, protect a 3rd place candidate?
> 
> It doesn't sound like much of a trade.
> 
> It isn't as if IRV could guarantee that a CW would win if s/he were 1st, 
> 2nd, or 3rd in favoriteness, while Runoff only guarantees that s/he wins 
> if s/he is 1st or 2nd. IRV makes no such guarantee. As shown above, IRV 
> can fail to elect a CW who is favorite to more people than any other 
> candidate is--even one who is favorite to about twice as many people as 
> any other candidate is.
> 
> In terms of concrete guarantees for electing a popular CW,  Runoff looks 
> better than IRV.
> 
> Isn't a 1st-placing or 2nd-placing CW more likely than a 3rd placing 
> CW--which IRV doesn't reliably protect anyway?
> 
> The Runoff proposal for state elections would be a big improvement over 
> Plurality, and seems to me to be better than IRV too. The Runoff 
> proposal should be supported unless we can get another, better, proposal 
> ready in time to compete with it. Or maybe just find out what happens 
> this time, and we can offer Approval or Condorcet next time.
> 
> Mike Ossipoff

-- 
  davek at clarityconnect.com    people.clarityconnect.com/webpages3/davek
  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
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