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Preferential voting does not satisfy the Condorcet criterion. http://en.wikipedia.org/wiki/Instant-runoff_voting#Voting_system_criteria http://en.wikipedia.org

Preferential voting does not satisfy the Condorcet criterion. http://en.wikipedia.org/wiki/Instant-runoff_voting#Voting_system_criteria http://en.wikipedia.org/wiki/Instant-runoff_voting#Voting_sy...

bradbeattie 14y ago
To demonstrate this, consider the following. 80 people: A, C, B 50 people: B, C, A 35 people: C, B, A IRV eliminates C (as it has the fewest first-place votes) and elects B. But voters on the whole prefer C over B (115 to 50). This is the failure that Pinckney refers to.
- deleted 14y ago
  [deleted]
finnw 14y ago
You mean IRV does not satisfy the Condorcet criterion. IRV is not the only preferential voting system. There are others, e.g. ranked pairs[1] which do. Under ranked pairs, each pair of candidates is considered individually, largest majorities first. In bradbeattie's example we have: C > B: 115 votes C > A: 85 votes B > A: 85 votes So the group preference is C > B > A and C wins. Ranked pairs fails the participation criterion[2], but it is still possible to vote tactically in a way that guarantees you will not harm your first-choice candidate by participating (since if your first choice is A you can rank A first and all the others joint second. Similarly if your goal is to prevent C from winning, you can rank C second and all others joint first.) [1]:http://en.wikipedia.org/wiki/Ranked_pairs http://en.wikipedia.org/wiki/Ranked_pairs [2]:http://en.wikipedia.org/wiki/Participation_criterion http://en.wikipedia.org/wiki/Participation_criterion
- Pinckney 14y ago
  Thanks. After looking into this, wikipedia provides a long list of things that can be referred to as "preferential voting." http://en.wikipedia.org/wiki/Preferential_voting http://en.wikipedia.org/wiki/Preferential_voting However, AFAIK, IRV is the system which most closely fits what gradstudent described.

Preferential voting does not satisfy the Condorcet criterion. http://en.wikipedia.org/wiki/Instant-runoff_voting#Voting_system_criteria http://en.wikipedia.org/wiki/Instant-runoff_voting#Voting_sy...

bradbeattie 14y ago

To demonstrate this, consider the following. 80 people: A, C, B 50 people: B, C, A 35 people: C, B, A IRV eliminates C (as it has the fewest first-place votes) and elects B. But voters on the whole prefer C over B (115 to 50). This is the failure that Pinckney refers to.

deleted 14y ago
[deleted]

finnw 14y ago

You mean IRV does not satisfy the Condorcet criterion. IRV is not the only preferential voting system. There are others, e.g. ranked pairs[1] which do. Under ranked pairs, each pair of candidates is considered individually, largest majorities first. In bradbeattie's example we have: C > B: 115 votes C > A: 85 votes B > A: 85 votes So the group preference is C > B > A and C wins. Ranked pairs fails the participation criterion[2], but it is still possible to vote tactically in a way that guarantees you will not harm your first-choice candidate by participating (since if your first choice is A you can rank A first and all the others joint second. Similarly if your goal is to prevent C from winning, you can rank C second and all others joint first.) [1]:http://en.wikipedia.org/wiki/Ranked_pairs http://en.wikipedia.org/wiki/Ranked_pairs [2]:http://en.wikipedia.org/wiki/Participation_criterion http://en.wikipedia.org/wiki/Participation_criterion

Pinckney 14y ago
Thanks. After looking into this, wikipedia provides a long list of things that can be referred to as "preferential voting." http://en.wikipedia.org/wiki/Preferential_voting http://en.wikipedia.org/wiki/Preferential_voting However, AFAIK, IRV is the system which most closely fits what gradstudent described.