From b77032006ce7d6350b4d756d875528aeab6efe92 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=C5=81ukasz=20Langa?= Date: Mon, 15 Oct 2018 06:03:29 -0700 Subject: [PATCH] [pep-8001] Define tactical voting --- pep-8001.rst | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/pep-8001.rst b/pep-8001.rst index c7569a941..95651840a 100644 --- a/pep-8001.rst +++ b/pep-8001.rst @@ -144,7 +144,35 @@ important decision like governance, we owe it to ourselves and the wider Python community to be transparent about how the choice was made. This removes ambiguity around *who* voted and *how*, as well as allows people to confirm whether any "tactical voting" occurred (which instant -run-off ranked voting is criticized for). +run-off ranked voting is criticized for; see below). + +Are there any deficiencies of instant run-off ranked voting? +------------------------------------------------------------ + +There is no perfect voting method. It has been shown by the +`Gibbard-Satterthwaite theorem +`_ +that any single-winner ranked voting method which is not dictatorial +must be susceptible to so-called "tactical voting". + +Tactical voting occurs when a voter supports a candidate against their +*sincere preference* in order to prevent an outcome they find most +undesirable. There are `four major tactical voting strategies +`_ +(compromising, burying, push-over, and bullet voting). + +Instant run-off ranked voting is resistant to burying and bullet voting, +while being somewhat vulnerable to compromising (less than the plurality +method) and vulnerable to push-over voting. Let's summarize those two: + +* compromising - the voter ranks a less desirable alternative higher + because they believe it has a higher chance of being elected; this is + sometimes called "casting a useful vote"); + +* push-over - if the voter is relatively sure their preferred candidate + will survive the first counting round, they may rank "the weakest" + alternative higher in the hope of that weak alternative being easily + beatable in a subsequent round. Copyright