FAIR-V: Difference between revisions
Simplified section on strategies
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First-Approval Instant-Runoff Voting (FAIR-V) is a [[Single Member system|Single-Winner]] [[Cardinal voting systems]] developed by [[User:Aldo Tragni|Aldo Tragni]].
The objectives of this voting system is the balance between simplicity, resistance to strategies, and elect the utilitarian winner.
==Procedure==
Voter score candidates with
# The candidate with the lowest sum of points is eliminated
===Normalization===
Using this norm, it's possible to apply the FAIR-V procedure also to ranges with more than
===Name derivation===
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* "Instant-Runoff": refers to the fact that, by eliminating one candidate at a time, only two will remain at the end, obtaining the "Instant-Runoff" (comparison of the top two candidates head-to-head).
FAIR-nV: the FAIR-V norm works with ranges of different sizes and n indicates the
*FAIR-1V: it's equivalent to AV, with ratings in [0,1].
*FAIR-V: is the default definition, with ratings in [0,
*FAIR-5V: uses ratings in [0,5].
*FAIR-9V: uses ratings in [0,9].
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===[[Tactical voting#Definitions|Min-maxing]]===
Properties of FAIR-V:
* increase rating of the candidate X in one vote doesn't change the chance of victory for candidates rated below the old rating of X.
* decreasing rating of the candidate X in one vote doesn't change the chance of victory for candidates rated below the new rating of X.
These properties mean that in FAIR-V a voter cannot favor a candidate more than the worst ones, by increasing his rating.
Example, given this honest vote:
if the voter only wanted to increase the chance of victory of B,C,D with respect to A, then vote like this is useless:
===[[Tactical voting#Voting_for_the_lesser_of_two_evils|Voting lesser of two evils]]===
Consider 2 frontrunners F1 and F2, among which the voter considers F1 > F2.
The properties indicated in the previous section ensure that the only interest of the voter is to decrease the rating of F2, leaving the rating of F1 unchanged.
If only F1 and F2 remain at the end of the count, it's sufficient only that those have two different ratings to ensure that the weight of the vote is maximum in favor of F1. This specifically ensures that F1 receives rating 0 if it's the worst candidate among all, or receives 1 if there are candidates much worse than F1 but not frontrunners (minorities); in both cases, the vote would remain very honest.
===[[Tactical voting#Pushover|Monotonicity failure]]===▼
Using the [[Yee diagram]] it was possible to observe that FAIR-V procedure is extremely resistant to the failure of monotonicity<ref>{{cite web|url=https://forum.electionscience.org/t/yee-diagramm-strong-monotonicity-failure-resistance/823|title=Strong monotonicity failure resistance|author=Aldo Tragni|language=en|access-date=1 September 2020}}</ref>, so the [[Tactical voting#Pushover|Push-over]] strategy can be considered practically absent.▼
==Voting systems comparison==▼
===[[IRV]]===
▲ A[0] B[1] C[2] D[2] E[3] F[5]
▲ A[0] B[0] C[0] D[0] E[0] F[5]
[[IRV]] assigns 1 point to the candidate with the highest rating, while FAIR-V assigns -1 point to the candidate with the lowest rating; both eliminate at each step the candidate with the lowest sum of points.
A big difference between the 2 types of counting is that in FAIR-V the failure of monotonicity is practically absent, while [[IRV]] is one of the systems in which it's most present.
▲===[[Tactical voting#Pushover|Monotonicity failure]]===
▲Using the [[Yee diagram]] it was possible to observe that FAIR-V procedure is extremely resistant to the failure of monotonicity<ref>{{cite web|url=https://forum.electionscience.org/t/yee-diagramm-strong-monotonicity-failure-resistance/823|title=Strong monotonicity failure resistance|author=Aldo Tragni|language=en|access-date=1 September 2020}}</ref>, so the [[Tactical voting#Pushover|Push-over]] strategy can be considered practically absent.
▲==Voting systems comparison==
===[[PRO-V]]===
FAIR-V is more resistant to strategies
==References==
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