User:Kristomun/Concorde

The Concorde method was a method used by the Debian project prior to their use of the Schulze method. It was defined in version 1.0 of the Debian constitution.

However, the legislative language is flawed. In the case of a Condorcet cycle, every candidate would have been eliminated by clause 3. Thus the instant-runoff voting tiebreaker only comes into play when there are actual pairwise ties, and the method is indecisive when faced with proper cycles.

In 2000, the Debian project established the Debian-EM Joint Committee to resolve these problems. Its members included Mike Ossipoff and Rob Lanphier of the election-methods mailing list.

Raul Miller first suggested an unnamed Smith-compliant method. The committee eventually settled on the Schulze method (Cloneproof Schwartz sequential dropping), which was ratified in the Debian constitution version 1.1 on June 21st, 2003.

Language

v1.0 of the Debian constitution stated:

1. [Concorde Vote Counting] is used to determine the winner amongst a list of options. Each ballot paper gives a ranking of the voter's preferred options. (The ranking need not be complete.)
2. Option A is said to Dominate option B if strictly more ballots prefer A to B than prefer B to A.
3. All options which are Dominated by at least one other option are discarded, and references to them in ballot papers will be ignored.
4. If there is any option which Dominates all others then that is the winner.
5. If there is now more than one option remaining Single Transferrable Vote will be applied to choose amongst those remaining:
   • The number of first preferences for each option is counted, and if any option has more than half it is the winner.
   • Otherwise the option with the lowest number of first preferences is eliminated and its votes redistributed according to the second preferences.
   • This elimination procedure is repeated, moving down ballot papers to 2nd, 3rd, 4th, etc. preferences as required, until one option gets more than half of the `first' preferences.
6. In the case of ties the elector with a casting vote will decide. The casting vote does not count as a normal vote; however that elector will usually also get a normal vote.
7. If a supermajority is required the number of Yes votes in the final ballot is reduced by an appropriate factor. Strictly speaking, for a supermajority of F:A, the number of ballots which prefer Yes to X (when considering whether Yes Dominates X or X Dominates Yes) or the number of ballots whose first (remaining) preference is Yes (when doing STV comparisons for winner and elimination purposes) is multiplied by a factor A/F before the comparison is done. This means that a 2:1 vote, for example, means twice as many people voted for as against; abstentions are not counted.
8. If a quorum is required, there must be at least that many votes which prefer the winning option to the default option. If there are not then the default option wins after all. For votes requiring a supermajority, the actual number of Yes votes is used when checking whether the quorum has been reached.

Notes

Erasing clause 3 would turn Concorde into Condorcet//IRV.

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