Each cohort knows that Carol is not a realistic threat to their preferred candidate, and will thus rank her second,
… except that you have her winning the election, which means that she obviously is a realistic threat, which means you don’t want to vote for her. Why wouldn’t the voters all assume that everybody else was going to do the same thing they were, thus making Carol a danger?
With a single vote per person, simple plurality feels like a fair result.
I don’t see why you’d say that. People are always complaining about it, and strategies for it are well known and constantly discussed every time an election comes around.
I also think that the example isn’t perfect (although I haven’t formalized why yet). But, you’re describing tactical voting, which is considered one of the “downsides” of RCV.
You’re already being tactical when you decide that Carol isn’t a threat and (falsely) uprank her. What changes if you go a step further to decide that she is a threat?
In fact, I think that the standard formalism for defining “tactical voting” is in terms of submitting a vote that doesn’t faitfully reflect your true preferences. Under that formalism, falsely upranking Carol is tactical, but switching back to your true preferences because of what you expect others to do actually isn’t tactical.
… and it’s odd to talk about tactical voting as a “downside” of one system or another, since there’s a theorem that says tactical voting opportunities will exist in any voting system choosing between more than two alternatives: https://en.wikipedia.org/wiki/Gibbard–Satterthwaite_theorem . At best you can argue about which system has the worst case of the disease.
And, if you’re comparing the two, plurality has a pretty bad case of tactical vulnerability, probably worse than IRV/RCV. That’s why people want to change it: because tactical voting under plurality entrenches two-party systems.
… except that you have her winning the election, which means that she obviously is a realistic threat, which means you don’t want to vote for her. Why wouldn’t the voters all assume that everybody else was going to do the same thing they were, thus making Carol a danger?
I don’t see why you’d say that. People are always complaining about it, and strategies for it are well known and constantly discussed every time an election comes around.
Personally I like range voting, though.
I also think that the example isn’t perfect (although I haven’t formalized why yet). But, you’re describing tactical voting, which is considered one of the “downsides” of RCV.
You’re already being tactical when you decide that Carol isn’t a threat and (falsely) uprank her. What changes if you go a step further to decide that she is a threat?
In fact, I think that the standard formalism for defining “tactical voting” is in terms of submitting a vote that doesn’t faitfully reflect your true preferences. Under that formalism, falsely upranking Carol is tactical, but switching back to your true preferences because of what you expect others to do actually isn’t tactical.
… and it’s odd to talk about tactical voting as a “downside” of one system or another, since there’s a theorem that says tactical voting opportunities will exist in any voting system choosing between more than two alternatives: https://en.wikipedia.org/wiki/Gibbard–Satterthwaite_theorem . At best you can argue about which system has the worst case of the disease.
And, if you’re comparing the two, plurality has a pretty bad case of tactical vulnerability, probably worse than IRV/RCV. That’s why people want to change it: because tactical voting under plurality entrenches two-party systems.