Is this variant of STV used anywhere else?

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The Politicus
Oct 06, 2021 02:45 PM 0 Answers
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In the rules of a political party in my (U.S.) state, a procedure for intra-party elections in which multiple positions are to be filled is described which is clearly a variant of the single transferable vote, but not a variant I have seen described elsewhere. (The identity of the party and state are not a secret, but I have not mentioned them here because they don't seem relevant.)

My question is: is this variant known or used elsewhere? Does it have a name?

If I understand the rules correctly, they are in essence as follows (but I am not an official of the party in question and this summary is offered without any warranty):

  • Electors cast ballots in which they rank-order as many candidates as they wish.

  • Votes are counted in a random order, each vote being tallied for a single candidate.

  • When any candidate reaches the Droop quota (1 + floor(number of ballots / (1 + number of seats to be filled))), they are declared elected. Thereafter, that candidate's name will be skipped over on any ballot.

  • In some elections, the result is required to be balanced with respect to particular categories (e.g. gender balance, geographic balance, what have you). Once the available seats for a particular category have been filled, the names of any further candidates in that category will be skipped over on any ballot counted later.

  • Each vote is tallied for the highest-ranked candidate still in contention when the vote is counted (i.e. not yet elected, and not a member of a category whose positions have all been filled). If no candidates named on the ballot are still in contention, the ballot is exhausted and is not tallied for any candidate.

  • When all seats have been filled by candidates reaching the quota, any remaining uncounted votes are discarded. (The rules do not say it, but the arithmetic guarantees that the remaining votes could not affect the result.)

  • If the votes are all counted before all seats have been filled by candidates reaching the quota, any remaining seats are filled by selecting the candidates of the relevant categories who have the largest number of tallies.

This is clearly a single-transferable vote in the sense that each vote is tallied at most once and can be transferred from the voter's first preference(s) to another candidate with a lower preference. And like any STV method it produces a roughly proportional representation of groups within the electorate. Like several other STV methods, it chooses randomly which surplus ballots should be transferred to other candidates.

Unlike any other STV method I have read about, it is designed to work with a single pass through the ballots. (Having sat through the counting of ballots in such elections, while those in the meeting wait for the results so they can move on to the next item on the agenda, I think this is an extremely useful property, not to be discarded lightly.) A consequence of the single-pass property is that no candidate is ever eliminated (except by reason of category), so no vote cast for a no-hope candidate is ever transferred to another candidate; the only transfers come from the surplus votes of successful candidates.

Does this method of running an STV election have a name? Is it used anywhere else or is it unique to this one party in this one state?

Note (although people will comment on these questions whether I ask them or not) I am not asking whether this method has particular strengths (other than the single-pass property and those it shares with other STV methods) or weaknesses that should be noted.

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  • October 6, 2021