[EM] Filling a vacated seat using STV

[Greg Dennis]

The Proportional Representation Society of Australia recommends vacancies
are filled by the "countback" procedure. References:
[1] https://www.prsa.org.au/countbac.htm
[2] https://represent.org.au/countback/

As a practical matter, though, it's not always straightforward to recover
the quota of votes that elected the vacating candidate at the original
election and then perform the countback. There are other methods that are
not as ideal, but they're usually easier to implement and probably
equivalent for most cases in practice:
1. Rerun the election with the vacating candidate removed, as you
described, but declare the vacancy filled by the first candidate to reach
quota who was not elected in the original election.
2. Fill the vacancy with the next-highest vote getter from the original
election

We can all come up with examples where these methods are not ideal, but
might be practically acceptable, especially if the term of office isn't
particularly long.

Greg


On Wed, Apr 8, 2026 at 8:51 PM Luděk Belán via Election-Methods <
election-methods at lists.electorama.com> wrote:

> Thank you, but in your example, with the Droop quota (specifically quota
> 34) I also get candidate C as the new winner, yet the second winner comes
> out as candidate D or B because they have the same number of votes. With
> the Hare quota, the new winners are candidates C and B; thus candidate A
> would be replaced by candidate C. And is it possible to find a
> counterexample for the unrounded Hare quota?
>
> Luděk Belán
>
> ---------- Původní e‑mail ----------
> Od: Ross Hyman <rossahyman at gmail.com>
> Komu: Luděk Belán <LudekBelan at seznam.cz>
> Kopie: election-methods at electorama.com
> Datum: 9. 4. 2026 0:59:36
> Předmět: Re: [EM] Filling a vacated seat using STV
>
> 35: A > C > D
> 33 B > C
> 17 C > D
> 15 D > B
> Two winners: A and B win.
> Exclude A: C and D win.
>
> On Wed, Apr 8, 2026 at 5:27 PM Luděk Belán via Election-Methods
> <election-methods at lists.electorama.com> wrote:
> >
> > Hello everyone,
> > does anyone happen to know whether the STV method can be used to fill a
> vacated seat by recalculating the original vote while simply excluding the
> candidate who took that vacated seat? Could a situation arise where this
> recalculation would cause someone else to lose their seat?
> > Thank you.
> >
> > Kind regards
> >
> > Luděk Belán
> > ----
> > Election-Methods mailing list - see https://electorama.com/em for list
> info
>
> ----
> Election-Methods mailing list - see https://electorama.com/em for list
> info
>


-- 
*Greg Dennis, Ph.D. :: Policy Director*
Voter Choice Massachusetts

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