>The complaints against STV, as I recall, boiled down to "just likeIRV, STV will sometimes eliminate the wrong candidate". It is not monotonic, so sometimes you get spoiler effects and perverse incentives.
The orphan method is one step more complicated than IRV/STV, but it is still a "simple" method.
SO: I am wondering what effects you would get if you applied the orphan method's elimination rule to multiseat STV? How would the results compare with "Sequential STV" or "CPO-STV", both of which are complex and computer-dependent? If the orphan method significantly improves the performance of IRV, would it similarly reduce the>complaints here against STV? >---------------------------------- >John B. Hodges, jbhodges@ @usit.net
Some further comments. Most Condorcet-methods are "brute force" computationally. The first thing they do is do all possible pairwise comparisons. The multiseat method CPO-STV is likewise a "brute force" method; for an N-seat race, it first enumerates all possible n-candidate ensembles, then makes all possible pairwise comparisons between them. (It somehow deduces from the voter's ballots ranking individual candidates which of each pair of ensembles would be preferred; I'm sure it also has some method of breaking ties and cycles.)
By contrast, Rob LeGrand's "orphan" method does not do all possible pairwise comparisons; it does only a minimal number of them. It is so computationally efficient that it is within range of a hand count if necessary.
Rob's "orphan" method is IRV with a different elimination rule; instead of eliminating the last-place candidate, do a pairwise runoff of the bottom two candidates and eliminate the loser. This is sufficient to prevent IRV from eliminating a Condorcet-winner, which in turn is enough to guarantee that it will pick the Condorcet-winner if one exists.
I am not a computer-science major, but I have heard of the "traveling salesman" problem and how it is computationally very expensive to guarantee finding the ideal solution, to the point of being practically impossible for large numbers of cities. But, I have also heard, there are simple algorithms that will reliably get you "close" to the ideal solution: for example, start where you are, and go to the nearest city you have not yet visited; repeat until you have visited all cities.
CPO-STV is an awesome multiseat method, conceptually. I'm wondering if there is a computationally efficient way of arriving at the same "ideal" ensemble. My "For Dummies" guess is that the ideal ensemble will never include a Condorcet loser and will always include a Condorcet-winner if one exists. STV with Rob's "orphan" elimination rule would (I guess) be sufficient to do that much.
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From: Markus Schulze Subject: Re: [EM] Cheering for simplicity/Orphan
I suggest that when there are N seats then at each stage a plain vanilla STV count should be hold between the N+1 candidates with the lowest numbers of first preferences and the loser of this count should be eliminated.
Markus Schulze
This is a fair multiseat analogy to Rob's single-seat elimination rule, but I don't immediately see any logical connection to finding the "ideal" ensemble (defined the same way as in CPO-STV.) I'd like to hear more about this idea.
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The reason this topic is interesting, IMHO, is that IMHO for selling a method to the American electorate, it would be advantageous to find a "unified method", one where the same basic algorithm would apply both to single-seat races and to multiseat Proportional Representation. STV has this. Approval and Condorcet have it, sort of, but their multiseat versions are so computationally expensive as to be out of serious contention. The average voter is not a CompSci major. They don't know how computers work, they don't WANT to know how computers work; computers are mysterious, and every voter knows they are also insecure. Methods that are computer-dependent are therefore suspect as to their "legitimacy", a critical necessity.
I think "Generalized Bucklin" may meet the need for a relatively simple version of multiseat PR for Approval. Granted it is Majority Choice Approval, not plain Approval, but I think Approval advocates should be able to live with that. The voter has the option of casting a "plain Approval" type of ballot, and it would have the same effect as under plain Approval.
Similarly I think it possible that STV with Rob's "orphan" elimination rule, or some other method of about the same complexity, could be a relatively simple version of Condorcet PR. IMHO it is worth looking into.
-- ---------------------------------- John B. Hodges, jbhodges@ @usit.net Do Justice, Love Mercy, and Be Irreverent. ---- Election-methods mailing list - see http://electorama.com/em for list info
