[EM] Why I think IRV isn't a serious alternative

[Brian Olson]

On Nov 26, 2008, at 5:53 AM, Greg wrote:

>> Greg, you didn't actually say that IRV is good, you just said that  
>> it's
>> unlikely to be bad.
>
> Huh? One reason I think it's good in part because it's very likely to
> elect elect the Condorcet candidate, if that's what you mean by
> "unlikely to be bad." Some other reasons I think it's good is that it
> resists strategic voting, allows third parties to participate, and
> paves the way for PR.

And you get all those other good qualities in just about every other  
election method past 'pick one'.
And I should have flipped that around, 'unlikely to be bad' means that  
there's a definite chance that it will be bad.

>> Why bother with something that's unlikely to be bad when we can  
>> just as
>> easily get something without that badness?
>
> You can't get rid of "badness." Every system is imperfect. IRV is
> non-monotonic; Condorcet is susceptible to burial. So we're left to
> balance the relative pros and cons.

So, you discount and ignore the possibility that IRV will make  
systemically the wrong choice and behave chaotically, and I discount  
and neglect the possibility that some people will cast crazy rankings  
ballots.
Obviously I still think I'm making the more rational evaluation.

>> Oh, and actually it _is_ likely to be bad. See that first graph?  
>> See how
>> over thousands of simulated elections it gets lower social  
>> satisfaction?
>
> Brian, you're graphs are computer-generated elections that you made
> up. They aren't actual elections that took place in practice, which
> show a high unlikelihood of being bad. When your theory is a poor
> predictor of the data, it's time to change the theory, not insist the
> data must be different from what they are.

Given the substantial lack of data (pretty little real world rankings  
ballot data available), I think the simulations are still valid and  
interesting. The simulations explore a specific and small portion of  
the problem space in detail. I'm looking at races of N choices which  
are similarly valued by all the voters. It's a tight race. Actual  
elections haven't been that tight. But tight races are the interesting  
ones. When it's crunch time, those are the ones that matter. Almost  
any method can correctly determine the winner of a race that isn't  
tight. So, IRV has demonstrated in the real world that it can solve  
easy problems. So what? Why wait until it gets the wrong answer in a  
real election to admit that IRV can get the wrong answer? In matters  
of public safety that would be called a 'tombstone mentality'.