[Elections-committee] STV vs. Condorcet

Thierry Carrez thierry at openstack.org
Tue Oct 15 20:10:11 UTC 2013


Hi election committee,

I have a few insights on those various election systems due to past
experience and Monty suggested that I shared them with the group.

Ranked voting systems are intrinsically superior to first-past-the-post
or cumulative systems because they let you express a complex preference,
and adding more candidates doesn't disrupt your ability to express that
preference. In ranked voting systems, more choice is actually always better.

That said, all ranked voting systems are not created equal. You should
pick one based on the intended results.

STV is designed for proportional representation of factions. It favors
candidates coming from those factions at the expense of consensus
candidates.

Condorcet favors consensus candidates and "natural" winners (the
Condorcet winner), at the expense of giving each faction its representant.

In a very simplified and inaccurate summary, given B>A>C and C>A>B
ballots, STV tends to pick B&C while Condorcet tends to pick A.

There is not a "bad" system and a "good" system, choosing between them
depends on the intended results. If the election is all about factions
and giving them fair representation, then STV is better. If the election
is about individuals and picking the most consensual candidates, then
Condorcet is better.

I tend to think that for this specific election (directors representing
the individual members, not any faction), Condorcet would yield better
results.

NB: there is an experimental "proportional Condorcet" algorithm at CIVS
that might make the best of both worlds, but it hasn't been as
battle-tested as STV and Condorcet. We will be running the TC ballot
through it to see how it affects the results and report back. I don't
think such an experimental algorithm should be under consideration for
the Foundation board.

-- 
Thierry Carrez (ttx)



More information about the Elections-committee mailing list