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Which voting systems do not have tactical voting? Specifically, expressing your true preference on a ballot will not result in a less favorably outcome.

I'm looking at both multiple-winner and single-winner.

One that I know off already is random ballot, and dictatorial.

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    $\begingroup$ Hmm... I'm not sure if you know Arrow's impossibility theorem, and whether it makes your idea impossible or not. $\endgroup$
    – Asydot
    Sep 27, 2015 at 4:25
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    $\begingroup$ I suspect you've already seen the information in the Wikipedia article. $\endgroup$
    – joriki
    Sep 28, 2015 at 8:48
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    $\begingroup$ By Gibbard–Satterthwaite theorem, any resolute voting rule that satisfies Pareto and which is non-manipulable (i.e. doesn't have tactical voting) is necessarily a dictatorship. See theorem 3.1.2 in Social Choice and the Mathematics of Manipulation by Alan D. Taylor. $\endgroup$
    – Watson
    Nov 19, 2016 at 13:05
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    $\begingroup$ @Watson That should be an answer $\endgroup$
    – endolith
    Mar 14, 2017 at 1:14
  • $\begingroup$ @Watson yeah, it is $\endgroup$ Jul 25, 2017 at 18:56

2 Answers 2

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As @Watson pointed out, any Pareto-satisfying voting rule that is strategy-proof must be a dictatorship (i.e. one ballot determines the election, regardless of what any other ballots say.)

However note that there are dictatorial voting rules that many would argue are nonetheless "fair" in some sense. Consider the "random dictator" method: Select one ballot at random, and use that to determine the election. Everybody has an incentive to vote sincerely (in case their ballot is the one chosen) and the method is likely (though not guaranteed) to pick the "best" candidate in the sense of maximizing global utility.

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By Gibbard–Satterthwaite theorem, any resolute voting rule that satisfies Pareto and which is non-manipulable (i.e. doesn't have tactical voting) is necessarily a dictatorship. See theorem 3.1.2 in Social Choice and the Mathematics of Manipulation by Alan D. Taylor.

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