[EM] IRV vs Condorcet
davek at clarityconnect.com
Thu Jul 24 00:50:01 PDT 2003
Seems to me Condorcet has pretty well won this one within EM, as I believe
But, if I listen outside the door, IRV is making so much noise that few
realize Condorcet exists, let alone that it is a preferable competitor.
Perhaps we need to sort out the similarities and differences more
carefully, and get into more publicity.
SIMILARITY: BOTH do ranked voting, with identical ballots, intending to
identify the best liked candidate, and usually agreeing as to winner. As
we debate we concentrate on cases for which they differ, for those are the
cases which are a source for debate.
DIFFERENCE: While Condorcet compares EACH pair of candidates and develops
a matrix of pair counts to identify best liked, IRV puts emphasis on
patterns, giving preference to those that are ranked first. See example
below where B is much more popular than A, but IRV never sees this for C
is more popular than B among B backers - even though all these C backers
like B better than A.
Some call this an argument for IRV, claiming that those C votes were
against B. Could be, sometimes, but more likely is a simple minor
disagreement within B's party that does not create a smidgen of desire to
have A win.
Condorcet precinct results are a matrix small enough to publicize at
that level, as well as being summable and publicizable at any level,
including the whole district - even state level for governor. Even 10
candidates would be manageable for this - a 10x10 matrix.
IRV must forward a count of how many voters vote each pattern, or
take part in the counting by forwarding first the first rank counts, and
then forwarding changes as each loser is eliminated. Given 10 candidates
there are a zillion possible patterns to forward - too many to publicize
something understandable for many candidates at precinct level.
IRV can also offer an ugly surprise - a handful of absentee ballots
can change the order of attending to losers, resulting in changing winner
when there was no visible reason for expecting this. Absentee ballots
could also change the Condorcet winner - but this is possible only when
the candidates were close to a tie.
Condorcet cycles can also disturb some. Worth remembering that
members of a cycle are near ties, identified as beating all outside the
cycle. Thus, while there MUST be a predefined rule for resolving a cycle,
just as for resolving a true tie, this is not a reason for giving up on
Example, designed to show difference between IRV and Condorcet:
This is incomplete - one last ballot to count. Last voter votes:
A - odds are against this, and leaves us a tie problem.
B - IRV and Condorcet agree that B wins:
IRV - C becomes loser.
Condorcet - B>A and B>C.
C>B - disagreement:
IRV - B loses; C loses; A wins; GREAT unhappiness among B backers.
Condorcet - a cycle, B>A and A>C and C>B, but B>A is stronger
than C>B, so B backers are pleased.
Plurality - don't know why anyone reads this far if they are not
ready to move on for something better.
Reruns of any sort - ask the French if these are not risky, while
Approval - actually more complex for the voter than ranked voting -
all that is needed for rank is better vs worse, Approval requires judgment
as to cutoff, but does not let the voter express the ranking required to
get this far.
PR - debate this another day - for the moment I am staying with
elections with single winners, and not concerned with legislatures where
PR MIGHT make sense.
Others - reject most for being complex, hard for voter to
understand, and/or being subject to strategies.
Condorcet method details:
Seems correct and agreed that voters can give identical rank when
candidates seem to deserve it. If it matters to the counting, give each
candidate of a pair half a win (remember that Condorcet is doing only one
pair at a time - 3 equal candidates will tie in 3 pairs). IRV could be
unwilling to touch this one.
Seems right and agreed that voters not be required to rank all
candidates - all not ranked are tied for last (except I would not count
even half wins among these).
Seems right to me that a voter should not be required to use every
rank - rank 2 is better than rank 4, and it should not matter when looking
at these two whether there is a 3.
While IRV gets away from most of Plurality's spoiler problems, it
has a few of its own. Condorcet simply DOES NOT DO spoilers.
Condorcet's matrices do not seem to get the positive attention I believe
they deserve. Because they are distorted little, if at all, by thoughts
of spoilers or voting strategy, counts for minor candidates warn:
Winners how serious they need to take these as warnings.
Minor candidates whether they need to change their approach.
IRV backers claim: "requiring a majority of votes to win" - seems like a
If they forbid truncation (an ugly thought), they could get there -
by sometimes including ballots in which the voter showed dislike of the
winner by ranking that candidate as that voter's almost last choice.
With truncation permitted, a majority of the ballots could have been
exhausted before they declare a winner from the remaining minority of the
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.
More information about the Election-Methods