On Sep 16, 2009, at 3:20 AM, James Gilmour wrote:
Jonathan Lundell > Sent: Wednesday, September 16, 2009 12:18 AM
In fact, a special provision must be made to ensure that previously
elected candidates remain elected in a countback. There are at
least a
couple of ways to accomplish this. It ends up being a subtle problem.
Jonathan, that's a helpful clarification. Does OpenSTV include such
"special provisions", so that it can cope with "count-back" counts
as well as counts where there are "withdrawn" candidates?
No, I don't think it does. And the standard input file format that we
use doesn't have a provision for marking candidates as protected,
either (though offhand I can think of a simple way of extending it).
These days, OpenSTV is pretty easily extended (we've moved to a plugin
architecture), so I suppose the real reason there's no support for
this is that we don't have any real-world rules to look to.
(It's also worth noting that additional candidates might choose not
to
stand, or be ineligible to stand, in the countback, and would need to
be marked as withdrawn as well.)
Yes, that would be the expected approach for STV count-back, as it
is in party-list PR systems where the casual vacancy is filled by
the "next" candidate of the relevant party.
James
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