[Alex Martelli <al...@google.com>]
> While I suspect most participants are aware of this, just in care some
> don't I thought I'd just point out that it's futile to look for a "perfect"
> voting system -- Kenneth Arrow proved that long ago, see
> https://en.wikipedia.org/wiki/Arrow%27s_impossibility_theorem
>
Yup! Ping's page acknowledges that explicitly:
http://zesty.ca/voting/sim/
and goes on to explain why he doesn't care ;-)
"""
...so one can always invent situations where a particular method violates
one of these criteria. Thus, presenting individual cases of strange
behaviour proves little.
A more substantive way to argue for or against a particular election method
would be to compare how frequently failures occur, under what conditions
they occur, and how severe they are.
"""
Which his visual simulations go on to do. Even a brief glance strikingly
shows that IRV frequently delivers outcomes that can only be called
"bizarre", not just that it's possible to contrive cases where one of
Arrow's criteria isn't met. For example,
"""
For four candidates in a perfect square (red, yellow, green, and blue at
(0.3, 0.3), (0.7, 0.3), (0.3, 0.7), and (0.7, 0.7) respectively),
Plurality, Approval, Borda, and Condorcet yield the obvious expected
outcomes here. But even in this simplest of cases, Hare behaves
unreasonably.
"""
So there's a real difference between perfection being unreachable and
behaving incomprehensibly in symmetric simple-as-possible cases no other
method has any problems with. As scenarios become more complex, IRV just
gets weirder.
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