To supplement Cam Gorgon's and David Shove's very helpful
explanations of the single-transferable-vote system, I offer the following
(slightly edited) excerpt from a report that I wrote for the Minnesota State
Bar Association, which last year adopted STV as its method of electing
officers and representatives:
STV is not necessarily a very simple way to run an election; indeed,
it is quite subtle. However, it sacrifices simplicity in favor of fairness,
efficiency, and diversity. Its fairness-to the individual voter, to each
group of voters, and to the candidate-far outweighs its subtlety.
STV implicates important choices of policy and principle. It is
easy to miss the forest for the trees by focusing too narrowly on the
mechanics of STV, rather than on these choices. The principle behind STV is
that representatives ought to reflect the makeup of the whole electorate
rather than the view only of a majority. The representative body ought to
represent a pluralistic census of opinions, not a consensus of opinion. A
more diverse, pluralistic representative body results.
STV is a form of preferential voting. Each voter ranks the
candidates in order of preference. A key concept in STV voting is the
"threshold" needed for election. The threshold is 1/(n+1), where "n" is the
number of representatives being elected. (This concept is already familiar
as the basis for the simple majority needed for election in a
single-representative election: if the number of representatives being
elected is one, the threshold is 1/(1+1), or 1/2.) Any candidate who
reaches the threshold is elected. In a multi-representative election, STV
gives a representative to any minority that can reach the threshold, rather
than let the majority (or even a mere plurality) control all the
representatives and exclude every minority candidate.
A simple analogy describes STV: Think of each candidate as carrying
a "bucket" to catch votes. The threshold is one full bucket. If a
candidate's first-choice votes fill the bucket, he or she is elected. If
nobody has a full bucket, the emptiest bucket is eliminated, and its
contents are poured among the other buckets according to the next choice on
each ballot. (This transferability of votes preserves each vote as long as
at least one candidate ranked by the voter is still in the running. It also
conserves the strength of any voting group, since each vote will migrate to
whichever candidate the rest of the electorate most prefers. Without this
step, too many candidates who appeal to the same group can split their
support into fragments too small to elect any of them.) This process
continues until one bucket fills.
If the fullest bucket overflows, the overflow is poured among the
other buckets. For example, if a bucket overflows by one-third, then only
two-thirds of each vote in the bucket was needed to exactly fill it up. The
remaining one-third of each vote is poured into the bucket of the next
choice on that ballot. (This step conserves the full strength of the vote,
so that there is no incentive for strategic misrepresentation. Without this
step, the voter may be tempted to rank a less-preferred but shaky candidate
over a more-preferred but safe one.) This process is repeated until all the
remaining buckets are full, or the number of buckets left equals the number
of spots to be filled.
BRM
Brian Melendez
St. Anthony West (Ward 3)
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