[Election-Methods] RE : Re: Borda-elimination, a Condorcet method for public elections?
jlundell at pobox.com
Sat Dec 22 12:56:25 PST 2007
On Dec 22, 2007, at 11:55 AM, Kevin Venzke wrote:
> --- Jonathan Lundell <jlundell at pobox.com> a écrit :
>> On Dec 22, 2007, at 6:45 AM, James Gilmour wrote:
>>> If you wish to utilise in some way all the information that could be
>>> recorded on a preferential ballot, that is a completely
>>> different voting system from IRV, with different objectives. The
>>> preferences are no longer 'contingency choices', but take on a new
>>> function depending on the detail of the voting system. It is almost
>>> certain that the voters would mark their ballots in a different
>>> way in an election by such a voting system from how they would mark
>>> their contingency choices in an election by IRV.
>> This seems plausible enough (and certainly IRV voters should be
>> instructed along contingency lines). WRT marking ballots differently,
>> setting manipulation aside, and considering only contingency vs
>> preferential ranking, do you have an example or two of how and why a
>> voter might end up with different ballots in the two contexts?
> I imagine James Gilmour is hinting at the fact that specifying lower
> preferences under Condorcet methods can damage higher-ranked
> candidates. So
> the Condorcet voter has to think about how far down to rank while
> the IRV
> voter should not have to.
> Not just voter incentives but candidate incentives will vary by
> too. Clearly certain types of candidates will not be viable under
> IRV but
> could be under Condorcet. It would probably be more safe to give a
> ranking to this sort of candidate under Condorcet than under IRV.
I can see that, more or less. STV and Condorcet are subject to
different kinds of manipulation, and that could influence a voter's
What I'm asking, though, is something else, and I concede in advance
that it's a fuzzy question, or perhaps one with an obvious answer.
Is there a case in which a voter's sincere ballot might differ between
an IRV (contingent choice) election, and (say) a Condorcet-compliant
election? I take James Gilmour to suggest that there might be, and
while it seems plausible to me that there might, I'm not able to think
of a clear example. It depends, I suppose, on what we mean by "sincere
ballot", and here the literature is not very helpful; it relies on the
intuitive idea that each voter has an ideal ranking of candidates,
possibly with ties, possibly with don't-cares.
It's easy to produce a counterexample for a multiple-seat STV
election. Here the voter must deal with two different contingencies:
my first choice might be eliminated, or my first choice might be
elected with a surplus. My sincere second choice might well be
different in those two cases; I might prefer A if only one of my top
choices is elected, but prefer B and C if two are to be elected (let's
say, for example, that B and C have complementary virtues, but that
either alone might be less effective than A in representing my views).
This problem doesn't arise in a single-seat STV (IRV/AV) election, of
At the moment, my guess is that in fact the a difference arises only
because of the different opportunities for manipulation presented by
the different voting systems, but the question of whether a voter's
sincere ranking might be different is intriguing.
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