[EM] IRV and Brown vs. Smallwood

[Juho Laatu]

--- On Wed, 8/4/09, Don & Cathy Hoffard <dchoffard at verizon.net> wrote:

> Thanks Peter for your comments
> 
> >Suppose that by my estimation about the electorate is
> about
> 
> >400: Smith, Jones, Johnson
> >300: Jones, Smith, Johnson
> >600: Johnson, Jones, Smith
> 
> Johnson loses regardless as to whether Smith or Jones is
> eliminated
> Normal IRV with no strategy:
> Jones is eliminated in the first round and Smith wins in
> the second round.
> 
> IRV with a strategy, of 101 vote switch, from Johnson
> voters to Jones 
> Smith is eliminated in the first round and Jones wins in
> the second round.
> The Johnson voters would have to except Jones as their
> second best choice.

Here's another way to describe this strategy.

If there is a Condorcet winner that will be
eliminated before the last round, then some
of the IRV voters have an interest to
compromise and vote for the Condorcet winner.
This group is large enough to make the
Condorcet winner win.

This strategy is also quite free of risks. In
the example above, if the Johnson supporters
are certain that Johnson will not win, then
they could all vote for Jones. If the last
round will be between Jones and Smith, Jones
will win anyway.

Actually it may be a quite good strategy in
IRV not to rank those favourite candidates
that do not have a chance but to rank only
those candidates that have a chance. This
increases the probability that one's most
favoured candidates with chances of winning
the election are not eliminated too early
(assuming that they might win if they could
stay in the race until the end).

Juho