If you're a member of the party establishment in one of the big two parties of a system, you stand to lose a lot by moving to an instant runoff and nothing to gain.
Unfortunately, most of the power to change the voting system is in the hands of these kinds of people, so it's going to be pretty hard to change it. Kind of a Catch-22.
I understand that things get a bit muddled because the individual representatives are also members of the electorate, and thus they may have warped incentives relative to the vast majority. But they are such a small fraction of the overall electorate that we should be able to ignore them in any kind of efficiency discussion.
I mentioned it because you said something about Pareto efficiency, and moving to instant runoff would not be Pareto efficient because some people (the parties are made up of people, remember) would be worse off.
Declaring something Pareto efficient has a specific meaning, and it applies to all people, not all the people that stanleydrew thinks are important. Though it's a comparatively small number of people, it's not some weird edge case that can be discounted. Rather, these are precisely the best people to convince to get the law changed. Note well that even this story in Maine, the measure was passed by ballot initiative, not by a legislature vote.
I am talking about the efficiency of the voting system itself, and its ability to express the preferences of the electorate.
Note that I'm not talking about changes related to the election outcomes that such a shift in voting systems would potentially cause.
Put another way, it would seem to be efficient to move to any voting system that would allow a voter to express more preferences than just one, since then we're getting strictly more information.
1. If every voter prefers A over B, the electorate prefers A over B
2. If no voter changes preference between A and B, the electorate's preference of A and B is unchanged
3. No single voter can always change the electorate's preference
This actually isn't true, because major party candidates will be worse off, but I think he meant something like Hicks-Kaldor efficient, or positive sum.
I am also seeing several comments that try to take into account the preferences of the candidates themselves, or their parties. Why? Aren't we talking about efficiency from the perspective of the electorate? To the extent that the candidates are themselves members of the electorate, and can vote for themselves, shouldn't we ignore them in this analysis because their preferences are inherently biased?
I fully agree with you. I was just being precise in my usage of Pareto efficiency, which includes all agents in a situation. Especially because it's used so often when Hicks-Kaldor improvement is meant (which means that there's the possibility for Pareto improvement after redistribution of gains).
As an impractical example, if you could get every voter to tell you exactly how many utils a particular candidate is worth to them (maybe through complex incentives), as a quantity and not as a ranking, you would end up with a perfect voting system.
As a more practical example, approval and range voting don't fall victim to Arrow's theorem.
Would end up with a perfect system, or could end up with a perfect system? I assume that latter, because I can easily design a system that uses that extra data and is far from perfect.
Assuming could, not would, my question then is that known? Or is it just known that Arrow's theorem does not apply to such systems, and so we cannot rule out that such a system could be perfect?