[EM] Instant 2-stage plurality/pairwise runoff

[Bart Ingles]

atarr at purdue.edu wrote:
> 
> As an interesting side note, the nation of Sri Lanka (just south of India)
> recently switched over to such an instant two stage runoff (we called it ITTR in
> a thread a few months ago, for instant top two runoff).  Thus far, their ITTR
> elections have produced the same results that a plurality election would have.
> It should be interesting to watch.  ITTR is better than IRV, although both are
> pretty bad.

ITTR sounds the same as the "Supplemental Vote" now used in London.  I
don't know whether it's better than IRV, but I would say it's
considerably worse than traditional Two-Round Runoff.  The reason is
that with ITTR, you need to be able to anticipate which second-choice
candidates will survive to the final round, otherwise your second choice
could be eliminated at the same time as your first choice.  With
traditional runoff, you get to see who's in the runoff before voting in
the runoff.

A simple change which would make ITTR more like traditional runoff would
be to let voters choose multiple second choices -- i.e. an approval vote
in the second round.  Then voters could vote for multiple candidates in
the runoff round, in hopes that one of them will actually be present in
the runoff.  Of course the risk would be of voting for *both* runoff
candidates.  But it would probably improve the overall social utility of
the winning candidate, vs. other traditional or instant runoff-based
systems (it would be interesting to see how well it does in
simulations).  I still wouldn't call it a good method though.

Bart