Potential For Tactical Voting
Like most voting methods, Condorcet methods are vulnerable to compromising. That is, voters can help avoid the election of a less-preferred candidate by insincerely raising the position of a more-preferred candidate on their ballot. However, Condorcet methods are only vulnerable to compromising when there is a majority rule cycle, or when one can be created.
Many Condorcet methods are vulnerable to burying. That is, voters can help a more-preferred candidate by insincerely lowering the position of a less-preferred candidate on their ballot.
Example with the Schulze method:
| 46 voters | 44 voters | 10 voters |
|---|---|---|
| 1. A | 1. B | 1. C |
| 2. B | 2. A | 2. B |
| 3. C | 3. C | 3. A |
- B is the sincere Condorcet winner. But since A has the most votes and almost has a majority, A can win by publicly instructing A voters to bury B with C (see * below). If B, after hearing the public instructions, reciprocates by burying A with C, C will be elected, and this threat may be enough to keep A from pushing for his tactic. B's other possible recourse would be to attack A's ethics in proposing the tactic and call for all voters to vote sincerely.
| 46 voters | 44 voters | 10 voters |
|---|---|---|
| 1. A | 1. B | 1. C |
| 2. C* | 2. A | 2. B |
| 3. B* | 3. C | 3. A |
- B beats A by 8 as before, and A beats C by 82 as before, but now C beats B by 12, forming a Smith set greater than one. Even the Schulze method elects A: The path strength of A beats B is the lesser of 82 and 12, so 12. The path strength of B beats A is only 8, which is less than 12, so A wins. B voters are powerless to do anything about the public announcement by A, and C voters just hope B reciprocates, or maybe consider compromise voting for B if they dislike A enough.
Supporters of Condorcet methods which exhibit this potential problem could rebut this concern by pointing out that pre-election polls are most necessary with plurality voting, and that voters, armed with ranked choice voting, could lie to pre-election pollsters, making it impossible for Candidate A to know whether or how to bury. It is also nearly impossible to predict ahead of time how many supporters of A would actually follow the instructions, and how many would be alienated by such an obvious attempt to manipulate the system.
| 33 voters | 16 voters | 16 voters | 35 voters |
|---|---|---|---|
| 1. A | 1. B | 1. B | 1. C |
| 2. B | 2. A | 2. C | 2. B |
| 3. C | 3. C | 3. A | 3. A |
- In the above example, if C voters bury B with A, A will be elected instead of B. Since C voters prefer B to A, only they would be hurt by attempting the burying. Except for the first example where one candidate has the most votes and has a near majority, the Schulze method is very immune to burying.
Read more about this topic: Condorcet Method
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