[EM] IRV vs RCV
robla at robla.net
Tue Dec 17 12:04:51 PST 2019
On Tue, Dec 17, 2019 at 9:19 AM [EST] robert bristow-johnson
<rbj at audioimagination.com> wrote:
> [At December 16, 2019 at 11:12 PM PST] Rob Lanphier <robla at robla.net> wrote:
> > I'm pretty sure all of the Condorcet-winner compliant methods chose
> > Andy Montroll, given the ballots from the Burlington 2009 election.
> > Copeland, Schulze, Ranked Pairs, etc. Was there a discrepency
> > between Condorcet methods, or just the well-documented discrepency
> > between the Condorcet methods and IRV?
> i misunderstood you. we're on the same page. yes, Burlington 2009 had a single, clear Condorcet winner.
Cool. I kinda figured it was a thinko, but I wanted to be
doubly-triply sure I check because I talk about Burlington 2009 so
> it was the only IRV election that i know of where the Condorcet winner was not elected.
It's the only municipal IRV election that I've independently confirmed
the discrepancy as well. But I haven't independently audited that
many municipal IRV elections.
I haven't analyzed /u/curiouslefty's claim that there was an
IRV/Condorcet discrepancy in Queensland Australia in 1998:
In general, though, my hunch is that others can be found. If
IRV/Condorcet discrepancies are truly one-in-a-million events under
real-world conditions, then we should stop obsessing about Burlington
2009, and get on board with
IRV/RCV/whatever-the-cool-kids-call-it-these-days. But if the number
is more like one-in-a-hundred or maybe three-in-a-hundred with a naive
electorate (i.e an electorate that probably hasn't learned how to vote
strategically), then that's an enormous problem. My hunch is that
it's closer to the latter, and that others can be found without too
much work because it's not that rare.
I'm aware of another ranked ballot election where there was an
IRV/Condorcet discrepancy: the 2003 Debian leader election. Debian
uses Condorcet-Schulze, so the pairwise winner won the election. But
intuitively, the result seemed to fall in the jagged borderline area
of Ka-Ping Yee's IRV simulations (that is, if we were talking about
that particular election as a datapoint in a simulation). Having
carefully analyzed both Debian 2003 and Burlington 2009, and then read
some of Ka-Ping Yee's research (and played with Nicky Case's wonderful
interactive version), I'm pretty sure that IRV is "stinky cheese" (as
Nicky Case puts it).
r b-j, thanks for advocating for BTR-IRV in Burlington! These
conversations inspired me to do a little clean up the BTR-IRV/BTR-STV
pages over on Electowiki:
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