Keeping Candidates in Subsequent Rounds of Instant Runoff Voting
Friday, August 12, 2016
3:05 pm CDT
Hi,
I'm a big time "newbie" here. Wasn't able, for some reason, to search the
existing messages so I thought I'd stick my neck out and ask a probably
stupid question.
In the IRV election method, I don't understand the rationale of eliminating
the lowest vote getter in each round. In a simple example, let's say there
are four candidates. Let's say A, B, and C get thirty percent of the vote
on the first round. Candidate D gets ten percent. Normally Candidate D is
eliminated even though s/he might be the choice of 90 percent of folks in
the second round.
Wouldn't it make sense to simply just leave everyone in each round and
continue to run the tally until someone has a majortity? If more than one
candidate, if the thing drug out, got a majority, one could use the one
that was the "most popular" (had the greatest total) at that point. If
there was a tie after at least two candidates had a majority, one could use
"drawing lots".
I'm sure there is something I'm missing here but the eliminating of a
candidate that might be basically relatively popular and a good compromise
candidate seemed to be a problem to me. Apologies if this one is totally
stupid. I've searched on-line without success at finding the answer. One
expert wrote back that it would cause problems but didn't specify what the
problems would be. Any help clarifying this for me will be appreciated.
Thanks,
York
Hello York,
It's not a stupid idea at all, it's intuitive and pleasing and I guess that many of us have thought of it. However, it damages one of IRV's major strengths, which means one can't propose it as a strict improvement.
The problem is that under IRV, you may vote "A>B" and have confidence that your vote for B will not be used until A is no longer an option. But if "eliminating" A does not mean that A is actually removed from contention, there is a possibility that your lower preference for B will help to elect B, when if you had only voted "A" (a bullet vote), the method would have elected A. This could cause voters to be more reluctant to express lower preferences.
This is not to say that I think the method is worse than IRV. It's just that it becomes a different type of method where there are a lot more ideas to compete with (many Condorcet methods, Bucklin, approval-elimination runoff, etc.).
Kevin
De : York W. &/or Lois G. Porter <porter@kih.net>
À : election-methods@lists.electorama.com
Envoyé le : Vendredi 12 août 2016 15h24
Objet : [EM] Keeping Candidates in Subsequent Rounds of Instant Runoff Voting
Friday, August 12, 2016
3:05 pm CDT
Hi,
I'm a big time "newbie" here. Wasn't able, for some reason, to search the
existing messages so I thought I'd stick my neck out and ask a probably
stupid question.
In the IRV election method, I don't understand the rationale of eliminating
the lowest vote getter in each round. In a simple example, let's say there
are four candidates. Let's say A, B, and C get thirty percent of the vote
on the first round. Candidate D gets ten percent. Normally Candidate D is
eliminated even though s/he might be the choice of 90 percent of folks in
the second round.
Wouldn't it make sense to simply just leave everyone in each round and
continue to run the tally until someone has a majortity? If more than one
candidate, if the thing drug out, got a majority, one could use the one
that was the "most popular" (had the greatest total) at that point. If
there was a tie after at least two candidates had a majority, one could use
"drawing lots".
I'm sure there is something I'm missing here but the eliminating of a
candidate that might be basically relatively popular and a good compromise
candidate seemed to be a problem to me. Apologies if this one is totally
stupid. I've searched on-line without success at finding the answer. One
expert wrote back that it would cause problems but didn't specify what the
problems would be. Any help clarifying this for me will be appreciated.
Thanks,
York
Election-Methods mailing list - see http://electorama.com/em for list info
On 08/12/2016 10:24 PM, York W. &/or Lois G. Porter wrote:
Friday, August 12, 2016
3:05 pm CDT
Hi,
I'm a big time "newbie" here. Wasn't able, for some reason, to search
the existing messages so I thought I'd stick my neck out and ask a
probably stupid question.
In the IRV election method, I don't understand the rationale of
eliminating the lowest vote getter in each round. In a simple example,
let's say there are four candidates. Let's say A, B, and C get thirty
percent of the vote on the first round. Candidate D gets ten percent.
Normally Candidate D is eliminated even though s/he might be the choice
of 90 percent of folks in the second round.
I'm not really a fan of IRV, and you're right that that is a problem.
IRV's elimination process ensures that you can't get the Condorcet
loser, but it by no means guarantees that you'll get the Condorcet
winner, as the Burlington election very easily shows.
I think IRV can be traced to STV, and that STV (the multiwinner version)
came first. STV's logic is to assign each vote to one of s candidates
(if there are s seats), and then elect those s candidates.
Finding out when a candidate has got enough voters to be elected is easy
enough: you just check if it's got a Droop quota or more of first
preferences. If so, exactly a Droop quota of votes can be considered to
have elected that candidate, and those votes are removed. This works
because if there are s seats, you can have no more than s Droop quotas'
worth of ballots in total.
However, when every candidate has fewer than a Droop quota's worth of
first preference votes, the above doesn't work. The easiest way to make
it work is to eliminate someone, because then the remaining votes will
be distributed over fewer candidates. But how?
STV chooses to resolve the problem by eliminating the candidate with
fewest first preference votes. It's the most natural way of doing it,
because then the criterion for who is going to be eliminated is based on
the same score (the plurality count) as the criterion for who is going
to be elected. For that reason, it's also relatively easy to manually
implement by shifting bundles of ballots around.
So if I were to guess, IRV is the way it is because it's a
specialization of a more general method (STV). And STV is the way it is
because it's based on quotas for election.
Wouldn't it make sense to simply just leave everyone in each round and
continue to run the tally until someone has a majortity? If more than
one candidate, if the thing drug out, got a majority, one could use the
one that was the "most popular" (had the greatest total) at that point.
If there was a tie after at least two candidates had a majority, one
could use "drawing lots".
That's more like Bucklin, which goes:
First round: count every voter's first preferences. If any of the
candidates has a majority, elect him.
Second round: count every voter's first and second preferences. If any
of the candidates has a majority, elect him.
.. and so on.
You could imagine this as holding multiple rounds where the voters
become less choosy as time goes on, and the moment someone gets a
majority, he wins.
I'm sure there is something I'm missing here but the eliminating of a
candidate that might be basically relatively popular and a good
compromise candidate seemed to be a problem to me. Apologies if this one
is totally stupid. I've searched on-line without success at finding the
answer. One expert wrote back that it would cause problems but didn't
specify what the problems would be. Any help clarifying this for me will
be appreciated.
Only taking first preferences into account makes IRV rather resilient to
strategic voting. But resistance to strategy isn't the only important
factor: performance under relative honesty is also important, and IRV
leaves something to be desired in that department.