[EM] RE : Ranked Preference benefits

[Juho]

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.

> 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. 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

Note also that at the first round vote R>>C>L gives exactly the same  
results as vote R>C=L. Ranked Preferences thus allows voters to  
"truncate" and in addition to indicate also the preference order of  
the "truncated" candidates. The lower strength preferences come into  
play after the higher strength preferences are no longer used.

It is also important from the R supporters' point of view to be able  
to indicate that C is better than L. They need to be prepared for the  
situation where R can not win. In example 1 C was eliminated first.  
With modified votes (see below) R will be eliminated first. Now the  
lower preferences of the R supporters become important. (first round:  
L=-10, C=0, R=-20; second round: L=-10, C=0)
20: L>>C>R
25: L>C>>R
30: R>>C>L
10: R>C>>L
15: C>L=R
If the 30 R>>C>L voters would have voted R>>C=L (truncated), L would  
have won. (first round: L=-10, C=0, R=-20; second round: L=-10, C=-50)

 From the A voters' point of view voting L>>C>R is also quite safe.  
Ranking C above R in the ballot does not help making C the winner  
(although it might make C a flat preference Condorcet winner) as long  
as L is in the game. And if L is eliminated, then these votes will  
support C over R.

I thus claim that truncation as a tool in traditional (flat  
preference) Condorcet methods is not as expressive and not as natural  
for the voters than the ranked preferences of the Ranked Preferences  
method. At least in this example voters clearly benefited of sincere  
voting.

I think it is a problem of basic Condorcet methods that they easily  
elect the centrist candidate. 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 (?). In  
some cases it allows also even more sincere ballots than the basic  
Condorcet methods (see above).

Juho Laatu

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