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I'm using OpenSTV's terminology for (Meek) single transferable voting, if it matters: "keep factor" is the percentage of votes for a winning candidate that are necessary to elect them (the remaining fraction is passed on to other candidates, if possible, or thrown away).

Suppose you have a multi-seat election with a fixed number of slots to rank candidates (perhaps 3-5 ranks available on the ballot) in which, when all seats are filled, one or more of the candidates has a relatively low keep factor (and was therefore overwhelmingly elected) of, say, 60%. What's more, the total of wasted votes is a sizable fraction of the threshold for election.

Is this outcome a significant problem for the election process that would justify modifying election policies to try to avoid it?

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    This is a pretty interesting technical question. I'm saddened that it hasn't received more attention or upvotes - this stack was designed for questions like this. – user4012 Aug 28 '16 at 23:30
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The Single Transferable Vote system was specifically designed to handle this situation. A low keep-factor on several candidates means that it was a very good decision to use the STV system for this election.

In STV, the voters can usually rank as many candidates as they want. There are multiple variants of how to count votes in an STV elections, but usually the situation in which a vote gets completely wasted is when all the candidates on a ballot reached the election threshold. The voter said "I want B, D and F, and nobody else" and that's exactly how their vote got interpreted by the system.

There are also counting variants where the votes of an eliminated candidate can not go to another eliminated candidate, so that's another way how votes can get discarded. When a lot of votes get discarded that way, it might be worth analyzing why some options appear very frequently on lower ranks but very rarely on higher ranks. Whether or not this is good or bad depends on circumstances and opinion.

In a non-transferable vote system, a very popular option often takes away votes from very similar options (the spoiler-effect) which results in the mainstream opinion being under-represented in the resulting parliament. But in a transferable system, people who vote popular options can still set the similar options as alternative choices, so these similar options aren't punished for following the mainstream opinion. This also limits tactical voting (I like all vowels, but I like A the most. But A is so popular they get over the threshold anyway, so I am dishonestly voting for E hoping to get a second vowel into the parliament).

For further watching I recommend the video "Politics in the Animal Kingdom: Single Transferable Vote" by CGP Grey.

But all of that only works properly when you allow voters to rank as many candidates as they like. When the number of ranks is artificially limited in your STV election and a large number of votes go to waste although they used all allowed ranks, then that's a sign that the number of ranks might have been inadequate to allow these voters to properly express their opinion and that it should be increased.

  • On the one hand, I think this answers my actual question very well; on the other hand, it does so by revealing a faulty hidden assumption that I've now edited into the question. – Nathan Tuggy Aug 25 '16 at 10:37
  • @NathanTuggy It's really not fair to change the premise of a question after you received a constructive answer based on the old premise. See "Question editing that invalidates answers" on meta. I nevertheless added an additional paragraph to address this. – Philipp Aug 25 '16 at 10:45
  • It's probably better to say "limits" rather than "prevents" tactical voting. It is really hard to come up with a voting system which can't be gamed by a very well informed voter under any circumstances, see eg. en.wikipedia.org/wiki/… – origimbo Aug 25 '16 at 10:45
  • @Philipp: Thanks for the updates. I really hate chameleoning myself, but under the circumstances I figured it was probably the least worst thing to do. – Nathan Tuggy Aug 25 '16 at 10:47
  • @origimbo That's correct. I edited the answer. – Philipp Aug 25 '16 at 10:48

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