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There's an upcoming election which features a particular candidate whose politics I have a problem with. Not only do I not want them to get in but I don't even want them to feel good or encouraged by getting a respectable count. If there was a form of anti-vote I'd be giving it to them. If my preferred candidate doesn't get in I'd have an "anyone but them".

The system is Proportional Representation / Single Transferable Vote. Once I've stated my preferences, I'd normally leave the rest of the ballot blank. My question is, is there any point in then proceeding to give a lower ranking vote to every other candidate, including the other ones I don't like, except this one as a kind of an anti-them vote? (e.g. to further reduce their chances or make them look bad in the count)

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    The exact voting method is going to matter here - you mention both PR (which most commonly refers to a party list system) and STV, the answer would be different for each. It also matters whether you are using the term STV casually to refer to any system where a vote transfers, or using the more formal definition which requires multi-member constituencies (if you have single member constituencies, the more correct term would probably be the Alternative Vote) – CoedRhyfelwr Feb 7 at 14:51
  • I would also include the voting system in the question title - if you need help determining the exact voting system, mentioning the particular election you;re asking about could help others determine it – CoedRhyfelwr Feb 7 at 14:52
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    @CoedRhyfelwr - it is indeed the single transferable vote with multi-member constituencies - it's the Irish election which takes place tomorrow. – colmde Feb 7 at 14:55
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Morally, I agree with the message of the other current answers that in the absence of more information on the intentions of your fellow voters, it is often worth honestly stating your full ordering of preferences for candidates under STV.

However it is worth noting that because the order in which candidates are eliminated influences the final result, the best stategy to answer

How can I best ensure candidate X doesn't win?

under STV can be any of:

  1. vote for the candidates in your honest order of preference,
  2. vote insincerely, favouring a lesser candidate or,
  3. not to vote at all,

depending on your knowledge of other voters' intentions.

To simplify the maths, lets assume only one seat is left (so that STV reduces exactly to IRV) and that we are down to three candidates, Y, Z and the dreaded X (none of these being ones you would ordinarily vote for). Then, reproducing an example from Wikipedia

Let's suppose you and a friend favour Y > Z >X, as do three other people. Four people favour Z > X > Y and six evil people think X > Y >Z.

If you and your friend vote, then the final round is a victory to X 10-5 over Y. If you both don't vote, the final round is a win for Z over X 7-6.

This kind of situation can occur when there are candidates clustered around extreme positions on multiple issues, less so when there is one major topic of disagreement.

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If you intend to do your utmost to ensure that this candidate does not get elected, it would be wise to rank every other candidate higher than them.

It is possible to think of an STV election as a series of voting rounds as candidates are eliminated and/or win seats. If the final "voting round" is between your two least favourite candidates (that is, everyone else has been eliminated or won a seat) your vote will only count if you have ranked everybody except your least favourite candidate. Ranking everybody is safe because STV satisfies the "Later-No-Harm" voting criterion. This means that ranking a later candidate can never harm a preferred candidate's chances of getting elected.

In short, you should rank everybody because in a small set of circumstances, it could hurt your least favourite, and it can never hurt your favourite.

(It is worth noting that if you want to stop your least favourite candidate more than you want your favourite to win, there are situations under STV where it is better to vote insincerely, or even not to vote at all. This is because ranking a candidate can hurt candidates that are ranked below them in unusual ways (see origombo's answer for more details). That said, these situations are really hard to predict so it's very difficult to actually act based on this information, and the correct course of action in most situations is to rank all candidates honestly.)

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  • How confident of the last sentence are you? While STV satisfies later-no-harm it don't satisfy the participation criterion, which covers the act of not voting in particular. en.wikipedia.org/wiki/… – origimbo Feb 7 at 16:04
  • But in this case, the voter has candidate(s) that they want to vote for - participation is not in question. The issue is whether, having voted for the preferred candidate(s), it is sensible to then rank the rest of the ballot. As I understand it, the Participation criterion would only come into play if the voter were thinking of not voting at all, which would be a different question. If the OP didn't have a preferred candidate and only wanted to stop one person, then this would come into play (although it's almost impossible to vote (or not vote) tactically around afaik) (cont) – CoedRhyfelwr Feb 7 at 16:56
  • but I don't think this is relevant to the question as it stands. I will add something to point this out when I get a a moment though, because it is interesting and related. – CoedRhyfelwr Feb 7 at 16:57
  • But once the candidates the OP actively wishes to vote for are knocked out, it does reduce to a participation question, to quote from the original question "Once I've stated my preferences, I'd normally leave the rest of the ballot blank." – origimbo Feb 7 at 17:17
  • I think it's more complex than it simply reducing to a participation problem, but I do see your point - that said, these situations are so hard to predict that it's more of academic interest than useful in a practical way. Thank you for pointing it out though, I would have missed it otherwise. – CoedRhyfelwr Feb 7 at 21:27
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Assuming you are talking about the Irish General Elections that are coming up (seeing your account states you are Irish) That works as follows:

The 160 members of Dáil Éireann will be elected by single transferable vote (STV) from 39 constituencies, each returning between three and five TDs (Dáil deputies). Voters complete a paper ballot, numbering candidates 1, 2, 3, etc. for 1st, 2nd, 3rd, etc. preference. Ballots are sent to the constituency count centre after polls close and are counted the following morning over several rounds. In STV, each ballot is initially credited to its first-preference candidate but may be transferred on later counts to the next available preference where the first preference candidate is elected or eliminated.

You should fill the entire list if you want to reduce a candidate's chance of winning as much as possible. The preferential ballot system is there to streamline the process of a multi stage election seeing that in this system it is possible for candidates to be eliminated before reaching the final nullifying all votes cast on the eliminated candidate.

Your preference list will matter seeing as your vote will go to next person in line if your candidate gets eliminated due to a lack of overall votes. This can repeat itself until no candidate you prefer is left leaving less opposition for the one you do not like increasing their chances of obtaining a spot. This way you ensure that your vote will not get tossed aside (and in effect reduce the % of votes your least favorite candidate gets).

A practical example would be the French election of 2017, in this election there were several parties in the first round with only the two largest going to the final round. In the first round Macron had 24.01% and Le Pen 21.30% meaning that as the two largest parties they would go to the final nullifying the other 54.69% of the votes. During the second election Macron got a total of 66.10% of the votes while 33.90% of the votes went to Le Pen.

Now in the second round people instead chose their "lesser evil", this caused a lot of people who dislike or don't agree with Macron to vote for him over Le Pen due to them disliking her even more. If they had chosen not to vote (out of protest) Le Pen could have become the winner (although the huge difference in the results would have made that unlikely).

The difference between this Irish election and that French election is efficiency, the French election was split up in two events while the Irish one is done in a single go (saving money and time in the progress). This ensures that you as the voter will never have an invalid vote, and although it might not be your preferred outcome it will reduce the chances of your "greater evil" obtaining a seat.

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    I think your answer is unclear. Your last sentence seems to suggest typubthinkbhat voting for everyone on the ballot except for one person increases that persons chance of being elected. If that's really what you are saying then I think you're incorrect. If you don't think that then can you rephrase. – Eric Nolan Feb 7 at 14:57
  • How the Irish system works is that they have several voting rounds with the same Ballot, if the OP's list is only filled with people who did not make it to the final rounds his vote becomes non existing. if he adds somebody he does not like but doesn't hate either that person will have a shot at getting an extra vote improving his chances against the person he does hate which could be the difference between that person getting a seat or not. If one of the persons he does like reaches then finales then the added preferences will become obsolete. – A.bakker Feb 7 at 15:02
  • but that means you did not understand his question, I think. that's precisely what he was asking about. likes A, hates Z. does not care for B-Y, normally would stop ballot after A. should he vote for B-Y just to spite Z? what are you saying, don't vote B-Y? or do vote B-Y? can't tell with your double negatives. unless I misunderstand STV, yes, vote B-Y because that puts all those folk on that list just a bit more ahead of Z. – Italian Philosophers 4 Monica Feb 7 at 15:06
  • @ItalianPhilosophers4Monica he asks if there is a purpose to fill in the ballot passed his preference if he want's a specific person not to win. If one of his preferred candidates makes it to the final, then no seeing the rest of the ballot would not be used. If non of his preferred candidates reaches the finales it would mean that somebody other then Z will get an extra vote improving that candidates chances of beating Z. – A.bakker Feb 7 at 15:09
  • so, should he fill in the rest of the ballot? yes or no? simple question. he doesn't know the outcome, no one does, yet. give a clear answer, then explain it, don't write something that explains the general mechanism and is unclear about your recommendation. that's Eric's point, I believe. – Italian Philosophers 4 Monica Feb 7 at 15:12
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It will come down to how popular your least preferred candidate is in the rest of the constituency.

If you think they are likely to get to a full quota in the first couple of counts, then expressing further preferences will do little to stop it, as they will already have been elected by the time your original preferences will have been exhausted.

If you think they will be in the battle for the final seat, your preferences are far more likely to play a role in that seat. If your preferences have been exhausted by this stage, then it does nothing for you. If you have indicated a preference for the other person, then your vote will count for that person.

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