[EM] RE : Ranked Preference benefits

[Chris Benham]

Juho,

Juho wrote:

>On Nov 2, 2006, at 1:29 , Kevin Venzke wrote:
>  
>
>>Juho,
>>
>>--- Juho <juho4880 at yahoo.co.uk> a écrit :
>>    
>>
>>>Example 1. Large party voters consider C better than the other large
>>>party candidate, but not much.
>>>
>>>45: L>>C>R
>>>40: R>>C>L
>>>15: C>L=R
>>>
>>>Ranked Preferences elects L. (first round: L=-10, C=-70, R=-20;
>>>second round: L=-10, R=-20)
>>>      
>>>
>>In my opinion, if C is able to convince *every voter* to acknowledge
>>that he is better than the major party alternative, then C is surely
>>not a bad result.
>>    
>>
>
>There is no need to convince every voter. This example is simplified  
>(for readability) but not extreme since there could well be a mixture  
>of different kind of votes. (See e.g. example 4.)
>
>The utility of C could be really low to the voters even though it was  
>ranked higher than the worst candidate (in Range terms e.g. R=99,  
>C=1, L=0). One of the key points of Ranked Preferences is that also  
>weak preferences can be expressed and they may have impact.
>  
>
CB: So in your example is electing C a "bad result" or not?!

>  
>
>>As long as truncation is allowed, and voters have the opportunity to
>>learn how the method works, I don't think "weak" CWs would be a real
>>problem.
>>    
>>
>
>I take this to mean support to basic (flat preference) Condorcet  
>methods with active use of truncation.
>
>  
>
>>If they're not "good enough" to win at all, people should not
>>be giving them votes.
>>    
>>
>
>I'd prefer methods where voters can simply vote sincerely without  
>considering when it is beneficial to truncate and when not. 
>
>  
>
Yes, don't we all.  You like methods  that  meet  Later-no-Harm  and  
Later-no-Help, so how
then is your method supposed to be better than IRV?

>Condorcet  
>voters need not leave non-approved candidates unlisted. I think  
>Ranked Preferences provides some improvements. I'll try to explain.
>
>If A and B voters would all truncate we would end up in bullet voting  
>and falling to a plurality style election. Not a good end result.
>45: L>C=R
>40: R>C=L
>15: C>L=R
>
>
>  
>
Since it gives the same winner as your suggested method, why not?

>
>I think it is a problem of basic Condorcet methods that they easily  
>elect the centrist candidate. 
>
>
>  
>
No, that is their theoretical strength. One big (over-looked by you) 
reason why  the "weak,
low-SU, centrist CW" is mostly a non-issue is that Condorcet methods 
create strong incentive
for "strong" high-SU centrists to be nominated.  This idea is well 
explained in James Green-Armytage's
July 2003 essay/post  "the responsiveness of  Condorcet".

http://lists.electorama.com/pipermail/election-methods-electorama.com/2003-July/010083.html

>If preference strengths are not known  
>electing the Condorcet winner is a good choice (and basic Condorcet  
>methods are good methods). If preference strengths are known, then  
>the choice is not that obvious. Ranked Preferences takes into account  
>the relative strength of preferences (but not the "absolute  
>strengths" in the Range style). The end result is more expressive  
>than basic Condorcet but still quite immune to strategies (?). 
>  
>
The "end result" is a horribly complicated, very awkward- to-operate 
monstrosity that we know
fails both Condorcet and  *Majority Loser* ( but you hope is "quite 
immune to strategies".)

I am a great fan of  "Definite Majority Choice" (DMC).
http://wiki.electorama.com/wiki/DMC

But suppose I was on the "same page" as you and thought that if  the CW 
is a "weak low-SU
centrist"  then it is desirable to elect a  "higher-SU" candidate, and 
also that the "ranked preference"
style of ballot you suggest should be used.  In that (hypothetical) case 
I suggest:

"Interpreting ballots as approving all candidates above the strongest 
indicated preference gap ("ties"
resolved by approving as many as possible without approving any ranked 
bottom or equal-bottom)
calculate the Definite Majority set (i.e candidates not pairwise beaten 
by a more approved candidate).
If  that set contains one candidate X only, elect X.

If not eliminate (drop from the ballots and henceforth ignore) the 
candidate with the fewest top (among
remaining candidates) preferences.
(I prefer above bottom equal-ranking to be not allowed, but if it is, 
then "fractional").

Recalculate (among remaining candidates) the DM set and repeat the whole 
process until an X is elected."

That at least meets  Majority Loser  and is relatively easy to operate. 
Also in common with IRV it meets
Dominant Mutual Third, Majority for Solid Coalitions and  Condorcet Loser.

>45: L>C>R
>20: C>>R>L
>35: R>>C>L
>
In this example you give your method electing L, failing  Majority Loser.

My suggested alternative (first) interprets the 45 L>C>R as L>C>>R and 
so calculates the initial DM set
as {C} and so elects C. If instead the votes were

45: L>>C>R
20: C>>R>L
35: R>>C>L

then all the candidates are in the initial DM set, so C is eliminated and then
the "new DM set" is {R} so R wins.



>Example 4. Some of the large party voters think C is good but  
>majority of them think C is no good.
>
>15: L>C>>R
>30: L>>C>R
>14: R>C>>L
>26: R>>C>L
>15: C>L=R
>
Initial approvals:  L45,  C44,  R40
C>R,  C>L,  L>R,  so initial DM set is {L,C}.
Initial top preferences: L45,  R40,  C15.

C is eliminated  and L wins  (agreeing with your method).


Chris  Benham



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