RE: Fw: Voting project

From: Arnie Urken <aurken_at_stevens-tech_dot_edu>
Date: Mon Aug 11 2003 - 19:11:13 CDT

Matteo and Doug,

"Preference" voting as you describe it is equivalent to "approval voting,"
expressing approval for one or more candidates by casting a single vote for
each choice. Approval voting is a ranked system with two sets: approved and
not-approved candidates. Note that under approval voting, there can be
plurality, majority, and unanimous ties, so make sure the code should be
able to detect such things.

Also, to force a "majority" winner in ranked, sometimes the choice that is
most frequently ranked in last place is deleted from all of the individual
voter rankings to produce a majority winner.

Arnie

-----Original Message-----
From: owner-voting-project@afterburner.sonic.net
[mailto:owner-voting-project@afterburner.sonic.net]On Behalf Of Douglas
W. Jones
Sent: Monday, August 11, 2003 1:58 PM
To: voting-project@lists.sonic.net
Subject: Re: [voting-project] Fw: Voting project

On Monday, August 11, 2003, at 02:27 PM, Alan Dechert wrote:

> Matteo,
>>
>> Can anybody shed some light on this topic?
>> I'm completely ignorant about "Instant Run Off Ballots"...
>>
> It's a form of ranked preference voting.

Right. One thing to beware of is that many people who advocate
instant runoff voting (or IRV as the proponents like to call it)
don't understand that there are a whole bunch of ranked-preference
voting schemes, of which IRV usually refers to only one.

In general, ranked preference ballots allow a voter to declare
first-choice, second-choice, third-choice, etc in a race. Some
ranked-preference schemes only allow a fixed number of choices,
for example, first and second choice, while others allow the voter
to make a complete ranking of all the candidates.

Each of the schemes listed below can be used in pure form, where
each voter is allowed to fully rank all N candidates in an N-way
race, and each scheme can be limited to only first and second
choice or some other fixed set of choices.

Given a set of ballots containing ranked preference votes, there
are a number of ways of declaring the winner. These alternatives
take, as starting points, the identical same ballots, but under
certain circumstances, they will declare different winners!

1) Weighted preference voting -- In this case, if the voter has
   cast votes (in ranked preference order) for N candidates, the
   top ranked candidate gets N votes, the second-ranked candidate
   gets N-1 votes, the third-ranked candidate gets N-2 votes, and
   the last ranked candidate gets 1 vote.

   Votes are totalled for all candidates independently. Whoever
   gets the most votes wins.

2) Weighted preference voting with bullet voting. You are allowed
   to vote for the same candidate as both first and second choice.
   In this case, you are said to be plunking all your votes on the
   same candidate instead of divvying them up between candidates.

3) Single transferrable vote (used in Ireland and Australia) --
   Stack the ballots in piles by the first-choice vote. Then, if
   no pile contains a majority of the ballots, take the shortest
   pile, and for each ballot in that pile, move it to the pile for
   the second-choice candidate on that ballot, since the first-
   choice on that ballot has been dropped from the election.
   If, at the end of this process, there is still no candidate with
   a majority, repeat this elimination process again.

   In effect, each voter is given one vote and is asked to list, in
   order of preference, the candidates to which that voter wishes
   his or her vote to be transferred. That's why this is called
   the STV system by its advocates in Europe and Australia.

   In the United States, it's usually called Instant Runoff Voting
   because each round of elimination can be thought of as a runoff
   election.

   If you limit the number of rounds in the election, the candidate
   with the most votes in the final round wins even if it isn't a
   majority. If some voter has only ranked their first K preferences
   and the Kth round doesn't give a winner, that voter's ballot is set
   aside and they don't end up participating in the final round(s).

4) Alternative instant runoff schemes, for example:

   If the first-choice ballot does not produce a majority for any
   candidate, the results of the first-choice voting for all voters
   are discarded and the second choice on the ballot is examined
   as a completely independent election. In this case, voters are
   permitted to vote for the same candidate as both first and
   second (and third) choice.

   If all voters vote identically in all rounds, this scheme is no
   use, but generally, supporters of minor candidates will tend to
   give a major candidate their vote in later rounds.

There are, of course, lots of other alternative ways to count
ranked preference ballots.

Unranked preference voting schemes also exist, notably preference
voting in which you can vote for as many candidates as you want,
essentially the same as plurality voting but with overvotes allowed.
In this scheme, whoever gets the most votes wins, but you can vote
for both Nader and Gore if you want, and it counts fully as one vote
for each.

                                Doug Jones
                                jones@cs.uiowa.edu
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Received on Sun Aug 31 23:17:08 2003

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