[EM] IRV in action

Dave Ketchum davek at clarityconnect.com
Wed Apr 2 09:44:10 PST 2003

On Tue, 1 Apr 2003 11:46:44 +0100 James Gilmour wrote in part:

 >>On Sun, 30 Mar 2003 22:38:15 -0800 Rob Lanphier wrote:
 >>>In this particular
 >>>election, there's no knowing how many of the 115 ballots accumulated by
 >>>Montgomery of Alamein (the runner up) in the 42nd round actually listed
 >>>Ullswater (the winner) next (who won with 151 votes).  If less than 61
 >>>ballots (i.e. 212 minus 151) of the 115 Montgomery of Alamein ballots
 >>>had listed Ullswater, then there was indeed no majority winner.
 >>Dave Ketchum replied
 >>Here you need to understand the language IRV uses - they LIKE the word
 >>"majority", treading lightly on the fact that they are doing a majority of
 >>the ballots that remain to be used to determine a winner, and not a
 >>majority of total ballots.
 > See my comment above.  Whatever other defects it may have, IRV does 
ensure that
 > the winner has the support of half or more of those who are voting at 
the point
 > when the final decision is made.  If some voters choose to drop out 
before the end
 > point is reached, that is their choice.  No one should claim more for 
IRV than can
 > be justified, but equally those who don't like IRV should not 
misrepresent the
 > results.
 >>With dozens of candidates (required to give 42 rounds something to work
 >>on), no voter should be required to rank every candidate, for it is
 >>unreasonable for voters to be expected to intelligently rank so many.
 >>Now, assuming A and B are liked better than the many Ms, and that some
 >>voters consider A and B to be less acceptable than any of the Ms they are
 >>prepared to rank, there will be ballots that are exhausted before we get
 >>to A vs B.  So the "majority" will simply be based on comparing A vs B,
 >>and be more than half of the ballots that included one or both of them in
 >>a voter's ranking.
 >>Oops, what I wrote above is not exactly right, but I choose to keep it in
 >>and correct it here:  Certainly ballots do get exhausted, so the majority
 >>to win is likely less than half the total ballots - it just has to be more
 >>than half the non-exhausted ballots.  So, if A has such a majority, then B
 >>and the remaining Ms, together, must have less, meaning that whatever
 >>might happen to the remaining Ms, A will still have a majority - and
 >>therefore the election can be terminated at this point without determining
 >>how decisively A won over B.

And, James agreed that, in rules he had codified, this termination is done.
 >>There was interest above as to whether some Montgomery votes might have
 >>listed Ullswater as a lower choice.  I see no value in this as these
 >>voters voted against Ullswater by listing Montgomery first.
 >>True IRV weakness that I see:
 >>      44 candidates got some first place votes and can, possibly, win -
 >>          even with two to get started with (candidates with only one
 >>could list them next).
 > I don't understand this comment.  What would the candidates list?

Let me try for better wording:  Assuming there was only one ballot listing
candidate X first, this ballot's second choice could have been Y, one of
the candidates that started with only 2 first choice votes.  This would
mean Y now has 3 votes, and possibly can advance as other weak candidates
are discarded and their votes reassigned.

 >>      Some of the above may have got only one - here the IRV counters
 >>decide which of these die now and which, if any, get a chance to advance.
 > What else can you do when you encounter a tie?  In the House of Lords 
 > election, the Returning Officer would appear to have made the decision 
to exclude
 > the tied candidates in alphabetical order.  Our regulations for public 
 > require the casting of lots to determine which of the tied candidates 
should be
 > excluded.

What you BETTER do BEFORE encountering a tie is expect them sooner or
later and provide rules.  That the Returning Officer apparently had no
guiding rule above implies a failure of the rule writers to complete their
job (being given an opportunity to write rules while holding the voted
ballots gives an opportunity to apply bias toward getting a personally
desired result).

 >>      37 got no first place votes.  These all die instantly, even if one
 >>of them got 400 second place votes - this happens because, whenever some
 >>of their second place votes get exposed, those will be discarded as lowest
 >>count among the remaining votes.
 > Are you seriously suggesting that electors would accept as the "winner" any
 > candidate who got NO first preferences  but lots of second preferences? 
  No matter
 > what social choice theory might say, I cannot see such a candidate ever 
 > accepted in a real election for public office.

YET, while IRV:
       Declares a candidate with ZERO first preferences an instant loser.
       It declares a candidate with TWO first preferences to have the same
theoretical chance to build strength with second (etc.) preferences as any
other candidate with two or more first preferences.

I do not see either of these candidates looking much better or worse than
the other.  If either got 400 second preferences, that one holds wide backing.

Take another look at the 2002 French elections.  We know that Chirac and
Le Pen get a bunch of first preferences and few if any second preferences.
   We know that a large field of candidates each gets less first
preferences, and loses by their rerun rules.  If the election had been
done by ranked ballots, there could have been a candidate in the field
that was acceptable to be winner, once you got past the candidates with
some first preference voting but no depth:
       IRV with luck:  the acceptable candidate survives and accumulates
preferences until winning.
       IRV with no luck:  the acceptable candidate gets crossed out during
some round, and therefore loses regardless of popularity.
       Condorcet:  here second preference counts ahead of all except first
preference.  If X, Y, and Z each only had first preferences ahead of 1/3
this candidates (A) second preferences, A is nearer to winning than any of
them (A>X is twice as frequent as X>A).  Even if A had no first
preferences, it should be more acceptable to the voters than any of X, Y,
or Z.

 > James

   davek at clarityconnect.com    http://www.clarityconnect.com/webpages3/davek
    Dave Ketchum    108 Halstead Ave, Owego, NY  13827-1708    607-687-5026
               Do to no one what you would not want done to you.
                     If you want peace, work for justice.

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