[EM] IRV vs Condorcet & Score?

[Dave Ketchum]

I wrote this to an audience considering IRV and talked of Condorcet  
for having almost the same ballot rules, but being better in other  
ways.  There are other methods also using ranked ballots, which I do  
not discuss here.


Range/score does ratings.  In its own way it lets voters vote for more  
than

one, and use ratings to easily indicate more and lesser preferences.

A quick comparison for voting for GOOD, SOSO, and BAD:  GOOD and BAD  
properly need high and low rank or rating.  SOSO requires different  
thinking:
 For Condorcet any rank above BAD and below GOOD will say all I  
can say.
 For Range/score if I rate it barely above BAD I risk it losing  
to BAD, depending on other voter ratings; if I rate it barely below  
GOOD I risk it beating GOOD, depending on other voter ratings.


Back to IRV:

I see IRV as an important topic, but have to argue against using it -
or for even promoting it and then suffering when those who learn that
it is less than perfect have nasty words for promoters.

What it offers voters is excellent - a voter can vote for more than
one, and can use ranking to easily indicate more and lesser
preferences.  These abilities are lacking in many election methods
such as Plurality, which is the method most of us have used most of
our lives.

Promoters can demonstrate the ease with which an election they choose
to demonstrate for IRV gets counted - discarding the candidates with
the least votes to correctly decide on the winner.

Those of us who have looked closer see what we call failures due to
IRV's way of making decisions with incomplete analysis, awarding wins
when complete analysis would declare a different winner - Burlington,
VT demonstrated this possibility recently in a real election.

I offer here an IRV demo - extreme, but showing what is too easy to
fail in a real election.  Here ALL like the Angel and Tom, Dick, and
Harry each have backers, so:
34 T>A>D>H
33 D>A>H>T
32 H>A>T>D
1   A

The 1 for A discards easily.  So do the 32 for H.  But this exposes 32
for A - which being low count gets discarded immediately.

So Tom wins with 66T>33D, though a closer look at the beginning would
have seen 68A>32H, 67A>33D, 66A>34T, 65H>34T, 66T>33D,  67D>32H.

I offer Condorcet, for which voters can vote exactly as for IRV but
have more complete analysis.  We can discuss more completely another
day.

Dave Ketchum



Election-Methods mailing list - see http://electorama.com/em for list info

Re: [EM] Uncovered set methods (Re: How close can we get to the IIAC)

[Jobst Heitzig]

Hi again Markus,

it's different. The goldfish winner can be really strange. If the defeat
strength are

   A  B  C  D
A  -  2  3  0
B  0  -  1  4
C  0  0  -  5
D  6  0  0  -

then Beatpath and Tideman give B, River gives C, and Goldfish gives D
since the table evolves like this:


  B  C  D
B -  1  0
C 0  -  0
D 2  3  -


  B D
B - 0
D 2 -


D
D   -

Yours, Jobst


Am 31.10.2010 18:35, schrieb Jobst Heitzig:
> Hi Markus,
> 
> on 29.04.2010 20:33 you asked:
>> is Jobst Heitzig's river method identical
>> to Blake Cretney's goldfish method?
> 
> I'm sorry that I have not read any list posts for months, so this caught
> my attention just now. I will check the differences! You probably refer
> to the method from Blake's Aug 12, 1998 post I cite below?
> 
> Yours, Jobst
> 
> 
> On Aug 12, 1998, Blake Cretney wrote:
>> Here's my entry for single-winner system of the week. It was motivated
>> by my desire to make a method that would be easy to program. To this
>> end, it does not require cycles or the Smith set to be found.
>> I'll call it "Goldfish" until someone shows me a previous mention
>> under a different name. The idea of goldfish is that the candidates
>> seem to eat each other, becoming bigger and bigger, until
>> only one is left swimming in the electoral fish bowl.
>>
>> Goldfish definition:
>> Successively find the worst defeat and eliminate the pair-wise loser.
>> Any win achieved by the pair-wise loser is now scored as if it was
>> achieved by the pair-wise winner, provided it is larger than the
>> one already scored by him, or he is currently scored a loss.
>>
>> Start by making a "victory" table. For each row, enter the votes
>> against each column's candidate, if the row's candidate wins
>> pair-wise. Otherwise enter a 0.
>>
>> The best way to resolve ties is for a chairman, president, or random
>> voter to enter a special ballot. This ballot must not be truncated.
>>
>> Repeat until only one candidate is left:
>> FIND:
>> Find the highest value in the table. Call this cell i,j. If
>> more than one row share this value, choose the row that is
>> higher in the special ballot.
>> MERGE:
>> Here's where the big fish eats the little one. For each cell
>> in the i row, if there is a higher value for that column in
>> the j row, copy it over. For each cell in the i column, if
>> there is a zero for that row in the j column, copy it over.
>> Do not change the empty cells on the diagonal.
>> ELIMINATE:
>> Remove the j candidate and its row and column from
>> consideration.
>>
>> I'm going to use the word "beats" to mean "defeats pair-wise" and
>> "eats" to mean "is chosen to defeat and merge with".
>>
>> MIIAC -- Candidates outside the Smith set are always beaten by
>> members of the Smith set. When they eat them, the rows and
>> columns are merged, but this provides nothing of use for beating
>> other Smith members, because candidates outside the Smith set only
>> have losing scores against those inside, and the merge rule does
>> not copy losing scores. This is because only 0 values are copied
>> from column to column.
>>
>> GITC -- If someone outside a clone set eats a clone, all the
>> clones will be eaten on successive rounds, just as if there was
>> only one. If a clone eats someone outside, the merge occurs.
>> Because the outsider loses to the clone, it can provide no help in
>> defeating other clones. It does not matter which clone eats an
>> outsider, because eventually all clones will be eliminated, or one
>> will eat all the others, and merge with them.
>>
>> GMC -- Because candidates are removed in order of votes against,
>> and because removal does not eliminate a majority vote against
>> a candidate, but merely copies it, candidates with a majority against
>> will be removed first.
>>
>> Elimination methods frequently have the problem that it is
>> possible to help elect a candidate by ranking it lower. This
>> happens when you can reduce the amount by which a victory is
>> obtained, so that a candidate is not eliminated, and can carry on
>> to defeat your enemies. The merge step in Goldfish makes this
>> strategy unnecessary. The winner ends up beating the same candidates
>> as the loser, and by as much. Lower losing values are not copied,
>> but having another candidate in the race with lower losing values
>> is not helpful.
>>
>> This seems like a pretty good system and is fairly easy to program.
>> With a couple of tweaks, it can be converted to Tideman.
> 
> 
> 
> Election-Methods mailing list - see http://electorama.com/em for list info

Election-Methods mailing list - see http://electorama.com/em for list info