[EM] IRV vs Plurality

[robert bristow-johnson]

On Jan 10, 2010, at 1:57 PM, Stéphane Rouillon wrote:

> from the data you produce, I agree that for the Burlington  
> election, IRV did produce the same result
> FPTP would have produced.

it's *not* the same result.  it is a worse result if you force the  
majority to vote strategically (which is what FPTP would do) than if  
you punish a minority for not voting strategically (which is what IRV  
did).  FPTP would have elected Kurt Wright to the dismay of 66% while  
IRV elected Bob Kiss to the dismay of far fewer because the Dems in  
Burlington like Progs more than they like GOPs.

> However, nobody can generalize this perticular case to any election.

but it *does* serve as a useful object lesson.

> I can observe that IRV allows more often to obtain a Condoret  
> winner when plurality fails, than plurality finds a Condorcet  
> winner when IRV fails.

well, that goes without saying.

> So I claim IRV is more reliable than plurality.

it saved Burlington from electing the 3rd most popular candidate and  
elected the 2nd most popular candidate.  the candidate preferred by  
the majority of voters (and thus would beat any other candidate in  
the final round had he been it the final round) was eliminated before  
the IRV final round.

it's a mixed result for the majority of Burlington voters.  but it's  
still better than Plurality or the Delayed-Runoff (which is what  
would happen if the old law was in force).

> Abd ul-Rahman Lomax a écrit :
>>
>> The recent election in Burlington, Vermont, though, was a partisan  
>> election. There, Kiss was trailing Wright in first-preference  
>> votes, but Kiss obtained enough vote transfers from Montrose  
>> supporters to pass up Wright in the second round of counting. Kiss  
>> is Progressive, Wright Republican, and Montrose is a Democrat.
>>
>> But looking at the actual voting data, which is available, we can  
>> see that Montrose was,

Abd ul,

the candidate's last name is "Montroll".  just thought i would point  
that out early.

(last October i presented a tutorial on finite-order polynomial  
approximation to transcendental functions and i mistakenly pronounced  
"Remez" with the "z".  that was embarrassing.  until discussing this  
with Terry B over tea, i had always pronounced the "t" in Condorcet.   
Terry has saved me from some wider embarrassment.

there's a joke we have here:

Q: What do you call someone who speaks two languages?
A: Bilingual.
Q: What do you call someone who speaks three languages?
A: Trilingual.

Q: What do you call someone who speaks one language?
A: American.




>> in fact, the Condorcet winner, and, as it's been pointed out, had  
>> a few of the Write supporters voted for Montrose in first place  
>> instead of in second, Montrose would have won. In other words, IRV  
>> will punish you (as does plurality) for voting your conscience;  
>> but with Plurality, it's obvious and everyone would know that  
>> voting for a Republican in Burlington would be a wasted vote

NOT necessarily.  that is not true.  Wright is presently a state  
legislator.  Wards 4 and 7 in the "New North End" (where i live) are  
predominately Republican.  in 20 years, Burlington could become more  
conservative.  or, in less time, the GOP could put forth an extremely  
competent and more moderate candidate for mayor where more Democrats  
would mark that Republican as their 2nd-choice than the Prog.

>> (where the leading party is Progressive),

that is not necessarily true.  but if you use 1st-choice mayoral  
votes as a guide, the Progs are the larger subgroup (Prog vs. Dem) of  
the larger group (liberal vs. conservative).  and it appears that IRV  
favors the majority of the majority (whereas Condorcet favors more  
the centrist)

>> so they'd have compromised and voted accordingly and Montrose  
>> would quite likely have won.

if a few hundred of these GOP Prog-haters would have just stayed  
home, Montroll would have certainly won.

>> Also, there is good reason to believe that most voters would vote  
>> according to the same patterns if the method were Bucklin.

one major complaint that people have against IRV (or Condorcet,  
though i do not think the complaint is justified against Condorcet)  
is that the tabulation method is complicated and not transparent  
enough.  it seems to me that Bucklin is even worse in that manner.

i still do not understand the objection to Condorcet.  it's  
conceptually simple, meaningful (reflects the will of the  
electorate), does not punish sincere voting, and is resilient against  
*common* strategy.

--

r b-j                  rbj at audioimagination.com

"Imagination is more important than knowledge."