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SecretMethod70 · 10-26-2004, 03:01 PM

When you're looking for the voting method that, statistically, is most likely to choose the candidate that most people can agree with, then hypothetical situations are very important. Current situations are easily covered in hypothetical situations. Looking strictly at the current situation, IRV is fine. But the goal is to find an election method which will result in the most preferred candidate winning under nearly all circumstances. When an election method provides such a clear and obvious method of strategic voting, it doesn't even come close to doing this.

IRV is the only seriously discussed voting method alternative that does NOT satisfy the <a href="http://en.wikipedia.org/wiki/Monotonicity_criterion">monotonicity criterion</a> - probably the single most important criterion that a voting system should satisfy.

It's far too long to quote in the thread, but you chould check out this page as well as it goes into the technical details a bit more and the various different tests which can and should be used to test voting methods: http://www.electionmethods.org/evaluation.htm

Here is what the evaluation page had to say about IRV regarding the monotonicity criterion. I felt that since this is the one I referred to in this thread I would provide it in here....

Quote:

Statement of Criterion

With the relative order or rating of the other candidates unchanged, voting a candidate higher should never cause the candidate to lose, nor should voting a candidate lower ever cause the candidate to win.
Complying Methods

All the methods listed in the compliance table above are monotonic except Instant Runoff Voting (IRV).
Commentary

In the ordinal methods (Condorcet, Borda, and IRV), a candidate is "voted higher" by being ranked higher. In Approval Voting, a candidate is "voted higher" by being "approved" rather than "disapproved." In a conventional plurality system, a candidate can be "voted higher" only by being voted for at all rather than not voted for.

Monotonicity is perhaps the most fundamental criterion for election methods. Common sense tells us that good election methods should be monotonic. Methods that fail to comply are erratic.

A simple example will prove that IRV is non-monotonic. Consider, for example, the following vote count with three candidates {A,B,C}:

8: A,C
5: B,A
4: C,B

In this example, eight voters ranked the candidates (A,C), five ranked them (B,A), and four ranked them (C,B). Candidate C was ranked first by the fewest voters and is eliminated. Since all the voters who ranked C first also ranked B second, B now has nine top-choice votes and wins.

Suppose, however, that two of the voters who had ranked A first reverse their first two preferences so their votes change from (A,C) to (C,A). Now the vote count is:

6: A,C
5: B,A
4: C,B
2: C,A

Candidate B is now ranked first by the fewest voters and is eliminated. Since the five voters who ranked B first also ranked A second, A now has eleven top-choice votes and wins. Hence, the two voters who demoted A from first to second choice caused A to win. That is, they caused A to win by ranking A lower, without changing the relative ordering of the other candidates. IRV therefore fails monotonicity.

For an even more bizarre example, consider the following vote count with four candidates {A,B,C,D}:

7: A,B,C
6: B,A,C
5: C,B,A
3: D,C,B

Applying the rules of IRV, candidate A wins. But suppose the three voters who voted (D,C,B) now promote A from last choice all the way up to first choice, without changing the relative order of the other candidates. Now B wins instead of A. So by promoting A from last to first choice, those voters caused A to lose instead of win. An election method that allows such nonsensical anomalies is erratic and should be rejected.

These are hardly contrived theoretical examples without practical relevance. IRV has serious problems both in theory and in practice. In practice, voters would soon realize, or be advised, that they cannot safely vote sincerely, and the political system would likely remain bogged down in a two-party duopoly just as it is today. And that is the optimistic scenario. If a third party somehow manages to become a strong contender, it could throw the entire political system into chaos, just as it could in our current plurality system.

This is just one criterion. Of 10. All of which IRV fails.

Clearly, it makes little sense for me to essentially rehash the entire site onto TFP. I don't expect the answers here to address every question every person may have. This is why I highly recommend looking at electionmethods.org and reading the ENTIRE site yourselves as well. It's not particularly a lot and shouldn't take more than a couple days if you spread it out.

There is also very useful information at www.condorcet.org although I have not had the chance to go through the entire site yet.