De Condorcet

DeCondorcet is a name that may be used for any voting system satisfying Condorcet's Criterion:

Any candidate who is preferred by a majority of voters to each other candidate should win.

I am not aware of anywhere in the world where such a system is in use. DebianGnuLinux uses DeCondorcet voting for their project leader and general resolution process.

For example, suppose

• 40 people vote ABC (i.e. they put A as their first choice, B as second, C as third)
• 10 vote BCA
• 10 vote BAC
• 40 vote CBA

Then B is preferred to A by a majority of 60 to 40, and to C by 60 to 40 as well. B was last on first preferences and would not win under InstantRunoffVoting.

The big problem is that a candidate meeting the condition need not always exist. (If one always did, ArrowsTheorem would be contradicted.)

For example, suppose

• 40 people vote ABC
• 30 vote BCA
• 30 vote CAB

This would suggest that a majority of 40 (70-30) prefer B to C, a majority of 20 prefer C to A and a majority of 40 prefer A to B. This situation is called a cycle.

Cycles are rare in practice, and can be resolved in a number of ways, suggesting that DeCondorcet could be used for public elections. However opponents argue that TacticalVoting can be used so as to create cycles and benefit from the cycle-breaker.

-- JoeOtten

Thanks a lot for the info. This does seem like a good VotingMethodCriterion; surprising to me that InstantRunoffVoting doesn't satisfy! -- BayleShanks

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CategoryVoting