Part of the Politics series |
Electoral systems |
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The sincere favorite or no favorite-betrayal criterion is a property of some voting systems, that says voters should have no incentive to vote for someone else over their favorite. [1] It protects voters from having to engage in a kind of strategy called lesser evil voting or decapitation (i.e. removing the "head" off a ballot). [2]
Most rated voting systems, including score voting, satisfy the criterion. [3] [4] [5] By contrast, instant-runoff, traditional runoffs, plurality, and most other variants of ranked-choice voting (including all strictly- Condorcet-compliant methods) fail this criterion. [4] [6] [7]
Duverger's law says that systems vulnerable to this strategy will typically (though not always) develop two party-systems, as voters will abandon minor-party candidates to support stronger major-party candidates. [8]
Instant-runoff voting fails the favorite-betrayal criterion whenever it fails to elect the Condorcet winner, a situation referred to as center-squeeze.
The favorite betrayal criterion is defined as follows:
The Center for Election Science argues systems that violate the favorite betrayal criterion strongly incentivize voters to cast dishonest ballots, which can make voters feel unsatisfied or frustrated with the results even after having the opportunity to participate in the election. [9] [10] [11]
Other commentators have argued that failing the favorite-betrayal criterion can increase the effectiveness of misinformation campaigns, by allowing major-party candidates to sow doubt as to whether voting honestly for one's favorite is actually the best strategy. [12]
Because rated voting methods are not affected by Arrow's theorem, they can be both spoilerproof (satisfy IIA) and ensure positive vote weights at the same time. Taken together, these properties imply that increasing the rating of a favorite candidate can never change the result, except by causing the favorite candidate to win; therefore, giving a favorite candidate the maximum level of support is always the optimal strategy.
Examples of systems that are both spoilerproof and monotonic include score voting, approval voting, and highest medians.
This example shows that instant-runoff voting violates the favorite betrayal criterion. Assume there are four candidates: Amy, Bert, Cindy, and Dan. This election has 41 voters with the following preferences:
# of voters | Preferences |
---|---|
10 | Amy > Bert > Cindy > Dan |
6 | Bert > Amy > Cindy > Dan |
5 | Cindy > Bert > Amy > Dan |
20 | Dan > Amy > Cindy > Bert |
Assuming all voters vote in a sincere way, Cindy is awarded only 5 first place votes and is eliminated first. Her votes are transferred to Bert. In the second round, Amy is eliminated with only 10 votes. Her votes are transferred to Bert as well. Finally, Bert has 21 votes and wins against Dan, who has 20 votes.
Votes in round/ Candidate |
1st | 2nd | 3rd |
---|---|---|---|
Amy | 10 | 10 | – |
Bert | 6 | 11 | 21 |
Cindy | 5 | – | – |
Dan | 20 | 20 | 20 |
Result: Bert wins against Dan, after Cindy and Amy were eliminated.
Now assume two of the voters who favor Amy (marked bold) realize the situation and insincerely vote for Cindy instead of Amy:
# of voters | Ballots |
---|---|
2 | Cindy > Amy > Bert > Dan |
8 | Amy > Bert > Cindy > Dan |
6 | Bert > Amy > Cindy > Dan |
5 | Cindy > Bert > Amy > Dan |
20 | Dan > Amy > Cindy > Bert |
In this scenario, Cindy has 7 first place votes and so Bert is eliminated first with only 6 first place votes. His votes are transferred to Amy. In the second round, Cindy is eliminated with only 10 votes. Her votes are transferred to Amy as well. Finally, Amy has 21 votes and wins against Dan, who has 20 votes.
Votes in round/ Candidate |
1st | 2nd | 3rd |
---|---|---|---|
Amy | 8 | 14 | 21 |
Bert | 6 | – | – |
Cindy | 7 | 7 | – |
Dan | 20 | 20 | 20 |
Result: Amy wins against Dan, after Bert and Cindy has been eliminated.
By listing Cindy ahead of their true favorite, Amy, the two insincere voters obtained a more preferred outcome (causing their favorite candidate to win). There was no way to achieve this without raising another candidate ahead of their sincere favorite. Thus, instant-runoff voting fails the favorite betrayal criterion.
![]() | This section is empty. You can help by
adding to it. (May 2024) |
A key feature of evaluative voting is a form of independence: the voter can evaluate all the candidates in turn ... another feature of evaluative voting ... is that voters can express some degree of preference.
Part of the Politics series |
Electoral systems |
---|
![]() |
![]() |
The sincere favorite or no favorite-betrayal criterion is a property of some voting systems, that says voters should have no incentive to vote for someone else over their favorite. [1] It protects voters from having to engage in a kind of strategy called lesser evil voting or decapitation (i.e. removing the "head" off a ballot). [2]
Most rated voting systems, including score voting, satisfy the criterion. [3] [4] [5] By contrast, instant-runoff, traditional runoffs, plurality, and most other variants of ranked-choice voting (including all strictly- Condorcet-compliant methods) fail this criterion. [4] [6] [7]
Duverger's law says that systems vulnerable to this strategy will typically (though not always) develop two party-systems, as voters will abandon minor-party candidates to support stronger major-party candidates. [8]
Instant-runoff voting fails the favorite-betrayal criterion whenever it fails to elect the Condorcet winner, a situation referred to as center-squeeze.
The favorite betrayal criterion is defined as follows:
The Center for Election Science argues systems that violate the favorite betrayal criterion strongly incentivize voters to cast dishonest ballots, which can make voters feel unsatisfied or frustrated with the results even after having the opportunity to participate in the election. [9] [10] [11]
Other commentators have argued that failing the favorite-betrayal criterion can increase the effectiveness of misinformation campaigns, by allowing major-party candidates to sow doubt as to whether voting honestly for one's favorite is actually the best strategy. [12]
Because rated voting methods are not affected by Arrow's theorem, they can be both spoilerproof (satisfy IIA) and ensure positive vote weights at the same time. Taken together, these properties imply that increasing the rating of a favorite candidate can never change the result, except by causing the favorite candidate to win; therefore, giving a favorite candidate the maximum level of support is always the optimal strategy.
Examples of systems that are both spoilerproof and monotonic include score voting, approval voting, and highest medians.
This example shows that instant-runoff voting violates the favorite betrayal criterion. Assume there are four candidates: Amy, Bert, Cindy, and Dan. This election has 41 voters with the following preferences:
# of voters | Preferences |
---|---|
10 | Amy > Bert > Cindy > Dan |
6 | Bert > Amy > Cindy > Dan |
5 | Cindy > Bert > Amy > Dan |
20 | Dan > Amy > Cindy > Bert |
Assuming all voters vote in a sincere way, Cindy is awarded only 5 first place votes and is eliminated first. Her votes are transferred to Bert. In the second round, Amy is eliminated with only 10 votes. Her votes are transferred to Bert as well. Finally, Bert has 21 votes and wins against Dan, who has 20 votes.
Votes in round/ Candidate |
1st | 2nd | 3rd |
---|---|---|---|
Amy | 10 | 10 | – |
Bert | 6 | 11 | 21 |
Cindy | 5 | – | – |
Dan | 20 | 20 | 20 |
Result: Bert wins against Dan, after Cindy and Amy were eliminated.
Now assume two of the voters who favor Amy (marked bold) realize the situation and insincerely vote for Cindy instead of Amy:
# of voters | Ballots |
---|---|
2 | Cindy > Amy > Bert > Dan |
8 | Amy > Bert > Cindy > Dan |
6 | Bert > Amy > Cindy > Dan |
5 | Cindy > Bert > Amy > Dan |
20 | Dan > Amy > Cindy > Bert |
In this scenario, Cindy has 7 first place votes and so Bert is eliminated first with only 6 first place votes. His votes are transferred to Amy. In the second round, Cindy is eliminated with only 10 votes. Her votes are transferred to Amy as well. Finally, Amy has 21 votes and wins against Dan, who has 20 votes.
Votes in round/ Candidate |
1st | 2nd | 3rd |
---|---|---|---|
Amy | 8 | 14 | 21 |
Bert | 6 | – | – |
Cindy | 7 | 7 | – |
Dan | 20 | 20 | 20 |
Result: Amy wins against Dan, after Bert and Cindy has been eliminated.
By listing Cindy ahead of their true favorite, Amy, the two insincere voters obtained a more preferred outcome (causing their favorite candidate to win). There was no way to achieve this without raising another candidate ahead of their sincere favorite. Thus, instant-runoff voting fails the favorite betrayal criterion.
![]() | This section is empty. You can help by
adding to it. (May 2024) |
A key feature of evaluative voting is a form of independence: the voter can evaluate all the candidates in turn ... another feature of evaluative voting ... is that voters can express some degree of preference.