[EM] IRV vs Plurality

[Chris Benham]

Dave Ketchum wrote (9 Jan 2010):

 
"For a quick look at IRV: 35A, 33B>C, 32C

A wins for being liked a bit better than B - 35>33.

That C is liked better than A is too trivial for IRV to notice - 65>35.

Let one B>C voter change to C and C would win over A - 65>35.

Let a couple B>C voters switch to A and C would win over A - 63>37.

Point is that IRV counting often ignores parts of votes.

Dave Ketchum"


Yes. 

The implicit assumption seems to be that "ignoring parts of votes" is 
always a pure negative but not doing so can cause failure of Later-no-Harm
and Later-no-Help, and vulnerability to Burial.

All Condorcet methods fail those criteria, while IRV meets them.

Note that I wrote that "IRV is my favourite of the methods that are
invulnerable to Burial strategy and meet Later-no-Harm".

I didn't write that it was necessarily preferable to to all of the methods
that meet the Condorcet criterion.

 
Chris Benham


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