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> Here they behave the same Well yeah, in this particular instance they do. That doesn't mean they always do. For example, with the commonly-used Tennessee c

> Here they behave the same Well yeah, in this particular instance they do. That doesn't mean they always do. For example, with the commonly-used Tennessee capital election scenario (https://en.wikipedia.org/wiki/Instant-runoff_voting#Tennessee_capital_election https://en.wikipedia.org/wiki/Instant-runoff_voting#Tennesse...), IRV would select Knoxville while FPTP would select Memphis - still not quite optimal for everyone (Nashville would probably be the ideal winner in a "perfect" electoral system), but good enough for the majority and a strict improvement over FPTP.

dllthomas 4y ago
Of course they don't always; certainly IRV is sometimes mechanically better. I believe we can construct examples where FPTP would happen to work out better given the same honest votes, although I do think they're more contrived - see below for details. I am more worried about what happens in practice, though; as I said, people understand with FPTP that they need to vote strategically and understand how to do that. Contrived scenario for FPTP picking the Condorcet winner while IRV fails to: Back to the "which theocracy, or do we just tolerance?" question, but now each religion has at least two candidates and secular tolerance has a bigger constituency. 19% S, ... 16% A1, A2, S, ... 15% A2, A1, S, ... 14% B1, B2, S, ... 13% B2, B1, S, ... 12% C1, C2, S, ... 11% C2, C1, S, ... FPTP picks S, sort of by chance, which is also the Condorcet winner. IRV consolidates the C votes behind C1, then the B votes behind B1, then the A votes behind A1, then discards S. I think that works out, FPTP makes the right choice for sort of the wrong reason while IRV makes the wrong choice. But I do think the much bigger concern is FPTP-with-strategic-voting behaving better (or at least no worse) than IRV-with-whatever-happens-in-practice.

dllthomas 4y ago

Of course they don't always; certainly IRV is sometimes mechanically better. I believe we can construct examples where FPTP would happen to work out better given the same honest votes, although I do think they're more contrived - see below for details. I am more worried about what happens in practice, though; as I said, people understand with FPTP that they need to vote strategically and understand how to do that. Contrived scenario for FPTP picking the Condorcet winner while IRV fails to: Back to the "which theocracy, or do we just tolerance?" question, but now each religion has at least two candidates and secular tolerance has a bigger constituency. 19% S, ... 16% A1, A2, S, ... 15% A2, A1, S, ... 14% B1, B2, S, ... 13% B2, B1, S, ... 12% C1, C2, S, ... 11% C2, C1, S, ... FPTP picks S, sort of by chance, which is also the Condorcet winner. IRV consolidates the C votes behind C1, then the B votes behind B1, then the A votes behind A1, then discards S. I think that works out, FPTP makes the right choice for sort of the wrong reason while IRV makes the wrong choice. But I do think the much bigger concern is FPTP-with-strategic-voting behaving better (or at least no worse) than IRV-with-whatever-happens-in-practice.