[EM] Fw: About non-monotonicity and non-responding to previous posts...

[Terry Bouricius]

Stephane,

In what way are you calling FPTP vote-splitting non-monotonic? It is
normally considered monotonic in that a voter raising the rank of a
candidate to number 1 can never hurt that candidate. Are you using the
broader non-standard definition of monotonicity that some particular
election method advocates have started using...where raising the rank of a
candidate to number 1 may hurt that VOTER'S interests (rather than that
first ranked CANDIDATE) by causing the election of that voter's least
favorite candidate. I have feel that is an overly broad expansion of the
concept of monotonicity, that some have seized on so they could claim
there are examples of non-monotonicity where there really aren't.

While I am one of those who thinks monotonicity is of relatively small
practical importance compared to certain other criterion, I think our
terminology definitions need to be standardized to allow us to understand
each other...and I would say IRV is a non-monotonic system and FPTP is
monotonic. Can you show that this is wrong?

Terry Bouricius

----- Original Message ----- 
From: "Stéphane Rouillon" <stephane.rouillon at sympatico.ca>
To: "Abd ul-Rahman Lomax" <abd at lomaxdesign.com>
Cc: <election-methods at lists.electorama.com>
Sent: Wednesday, November 04, 2009 11:20 PM
Subject: [EM] About non-monotonicity and non-responding to previous
posts...


Miss Dopp was promoting FPTP in the past, saying IRV is non-monotonic,
until I showed that FPTP vote-splitting behaviour is non-monotonic too.

> - more voters prefer B to C
> - a fraction of those voters will vote for A because they even prefer
> A to other candidates
> - thus C can get elected because of vote-splitting between A and B
>
> Even if more voters prefer B to C, the result is that C wins over B.
> This is clearly non-monotonic.
> This is a typical vote-splitting case using FPTP.

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