[EM] Question on RCV/IRV multi-seat method used in Minneapolis

[James Gilmour]

Kathy Doppn  > Sent: Tuesday, September 23, 2008 5:05 PM
> Do you or does anyone know if this multi-seat IRV method that
> splits votes of voters to their second choice candidates 
> after some winning candidates receive the threshold amount of 
> votes, exhibits non-monotonicity or not like the normal IRV 
> method does?  If so, is there an example posted somewhere?

All versions of STV used in public elections are non-monotonic, i.e. both single winner (IRV) and multi-winner (STV-PR in all
forms).  How frequently a non-monotonic effect arises in practice is a matter of some dispute.  See for example:	
Allard C. (1996)  Estimating the Probability of Monotonicity Failure in a UK General Election.  Voting matters, Issue 5, p1-5

  http://www.votingmatters.org.uk/ISSUE5/P1.HTM

Those who favour STV consider that criteria other than monotonicity are more important to voters, e.g. later no harm, and you cannot
have both.  One reason for not worrying too much about the non-monotonicity of STV in public elections, with large numbers of
voters, is that it cannot be exploited either by the candidates or by the voters.

If this question is not about STV-PR, but is about "multiple IRV", i.e. the repeated application of IRV sensu stricto to a
multi-seat election, I would not be at all surprised if that voting system were also non-monotonic.  However, "multiple IRV" has far
more serious defects than any failure of monotonicity and has nothing to recommend it.

James Gilmour