4

If I was to participate in a election using the Single Transferable Vote system, what would be my best strategy to try and prevent one candidate from winning.

For example if there are 5 candidates. One who I would like to win, one I very much would not like to win (Plus 3 who I don't have much opinion either way).

It is however most important to me that the one I dislike does not get in (I disagree strongly with their policies etc.)

What would be my best strategy?

  • Vote for all with Mr/Ms bad policy in last place?
  • Vote for all Except Mr/Ms bad policy?
  • Vote for just my top 1,2, or 3?
  • Something else?

Is there a difference if there is only one seat, or several seats?

  • 2
    Side note: general STV strategy is apparently NP-complete: diafaneia.ee.auth.gr/sites/default/files/stv.pdf – user4012 Jan 22 '14 at 23:40
  • And another difficulty with tactical voting in STV: votingmatters.org.uk/ISSUE1/P3.HTM – user4012 Jan 23 '14 at 0:07
  • 1
    Aside from my comments above, the answer may depend on STV counting rules – user4012 Jan 23 '14 at 0:08
  • Incidentally, the person I did not want to win, didn't Although in this case my voting strategy didn't make much difference. – DarcyThomas Feb 1 '14 at 2:50
  • 1
    As a general rule, STV is designed so people don't need to do tactical voting. The concept is harder to understand, but the process of using it tends to be simpler. – TRiG Feb 3 '14 at 18:43
5

Giving your last preference for a candidate and not voting for them at all are equivalent in all forms of STV that elect a fixed number of people.

Your first two options are therefore equivalent.

Leaving out more than one person runs the possibility that one of them might be excluded rather than the one candidate you strongly dislike when your vote could have reversed that.

If you're determined to vote tactically, you should vote for all candidates other than the one you want to lose in reverse order of their popularity, ie from least popular (with other voters) to most. This assumes that you have some knowledge of how other voters will vote. This strategy is designed to minimize the chance that your vote ends up in a surplus, and therefore minimizes the risk of your vote being reduced in value by being surplus-transferred.

[Footnote, you can use STV with a fixed quota rather than a fixed number of winners; this allows for constituencies to automatically adjust depending on turnout, but also means you don't know in advance how many winners there will be, as high turnout will increase parliament size. In that case, there is a difference between a full ballot and an all-but-one ballot; you should only include candidates that are better than no representative. I'm not aware of any election in which this system is actually used.]

  • Wouldn't not voting for them make it more likely for them to get eliminated before the end of the process, thereby accomplishing the goal? – Bobson Feb 7 '14 at 17:03
  • 1
    No, because your vote will never transfer to the last person on your ballot paper. – Richard Gadsden Feb 19 '14 at 10:16
  • Put that way, it makes sense. – Bobson Feb 19 '14 at 11:13
1

The standard form of Single Transferable Vote goes:

  • A candidate who has reached or exceeded the quota is declared elected.
  • If a candidate has more votes than the quota, surplus votes are transferred to other candidates. Votes that would have gone to the winner go to the next preference.
  • If no-one new meets the quota, the candidate with the fewest votes is eliminated and those votes are transferred.
  • This process repeats until either a winner is found for every seat or there are as many seats as remaining candidates.

While (as @DVK linked) there's no general strategy to elect someone, the bolded part is key to avoiding someone getting elected.

Since the remaining candidate with the fewest votes is eliminated first, you want everyone else to have more votes than the one you wish to be eliminated. That means casting a vote for everyone except the one you dislike.

  • I do not understand why this method it correct... especially since this is basically the same answer I provided that you said was wrong. – SoylentGray Jan 23 '14 at 15:20
  • 1
    @Chad - I never said your answer was wrong, I said it didn't reference STV. In this case, I quoted the rules that make up STV, and called out the specific one that will help to avoid someone getting elected. I can try to elaborate on it if it would help. – Bobson Jan 23 '14 at 15:23
  • The question was about the STV so of course my answer was referencing it and how the number there worked. This must be wrong. – SoylentGray Jan 23 '14 at 15:26
  • @Chad - Undelete it, then. I'll remove/clarify my comment. – Bobson Jan 23 '14 at 15:33
1

I've read through the article you've posted, and I think that you probably want to rank your vote in the order of likeliness to win, and simply not vote for the candidate that you don't want to get elected.(or if you have to rank him, rank him last.

Not only does this strategy maximize the chance of the person who you don't want to win to get eliminated, but It also maximizes the chance that other people get elected.


If you are correct in your analysis of who is the most likely to win, than your vote will always be helping elect someone who is not that candidate, and can fill all the seats before that candidate wins.

-2

There is no other sensible answer except to do what makes sense to do: rank your favorite candidate first and your least favorite candidate last. Anything else is nonsense.

  • 3
    Sorry, but that is a random guess containing numerous logical fallacies, not an answer. – user4012 Jan 25 '14 at 14:51
  • 1
    This would be accurate if and only if you were required to cast a vote for every candidate. But STV allows for a non-vote as well, which complicates matters and is the whole point of the question: Is it better to cast your lowest vote for the worst candidate, or better to cast no vote for that candidate? – Bobson Jan 27 '14 at 15:52
  • @Bobson: Actually, that assumption is not sufficient. Even if everyone is required to rank every candidate, there will still be insincere strategic voting. – Kevin Feb 16 at 18:04

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .