|
Science
October 12,
2001
Steven Brams and Dudley Herschbach are right about the
defects in the plurality voting system used in most U.S. elections
(Editorial, "The science of elections," 25 May, p. 1449). But, on
both theoretical and practical grounds, they are wrong to tout
approval voting (AV) over instant runoff voting (IRV).
Used for decades in Australia and Ireland and
considered in 13 U.S. state legislatures this year, IRV allows
voters to rank candidates in order of preference. A voter's best
strategy is to sincerely rank the candidates. If no candidate gets a
majority of first preferences, candidates at the bottom are
sequentially dropped. Each ballot cast for those eliminated
candidates is added to the totals of the next choice indicated on
that ballot until a candidate achieves a majority. IRV duplicates a
series of traditional runoffs, but without the need for additional
elections that cost taxpayers and candidates more money and often
lead to falloffs in voter participation (1).
In contrast, AV is a binary system, where the voter
can only indicate "yes" or "no" for each candidate. The problem is
that voters rarely have binary views about a range of candidates.
Assume a voter sees Z as most favored, Y as less favored, and X as
unacceptable. By voting for "acceptable" candidates Y and Z, the
voter could cause Z to lose. But by voting only for Z, the voter
makes it easier for X (the unacceptable candidate) to win (2). The
voter will be torn between voting defensively against X or
strategically for Z because voting for a second choice counts
directly against your first choice.
Approval voting has another important real-world flaw.
Political behavior has much to do with what is rewarded by the
election system, and AV would exacerbate one of the worst aspects of
U.S. campaigns: avoidance of substantive policy debate. Because a
candidate could lose despite being the first choice of an absolute
majority of the electorate (3), smart candidates would avoid
controversial issues that alienate any significant number of voters.
Smiling more and using policy-empty themes like "I care" will not
clarify the important choices leaders must make. Those rewarded by
AV could be characterized as "inoffensive" more than "centrist."
IRV strikes a better balance. It rewards candidates
who stand out on policy enough to gain first-choice support, yet
encourages coalition-building and fewer personal attacks as
candidates seek to be the second choice of other candidates'
supporters.
These arguments help explain why IRV
is used and proposed far more often than AV, and why next year
Alaska and San Francisco will hold ballot measures to implement IRV
for their major elections (see for
details). IRV is the right system for the United States' high-stakes
elections with a single winner.
Rob Richie
Terry Bouricious
Phillip Macklin
References and Notes:
1. Ireland's 1990 presidential race provides an
example of how IRV works. In the first round, Brian Lenihan won 44%
of first choices, Mary Robinson won 38%, and Austin Currie won 17%.
After Currie's elimination, Robinson had clear majority support. She
won 53% to 47% in the second round of counting. Without IRV, Currie
would have been a "spoiler" and handed the presidency to Lenihan.
2. Imagine an AV election with 100 voters. After 98
ballots are counted, the results give 55 approval votes to candidate
Z, 60 votes to candidate Y, and 61 votes to candidate X. The two
remaining ballots were cast by those voters who really liked Z and
intensely dislike X. If knowing these results in advance, they would
want to block candidate X by casting votes for both candidates Y and
Z. Now suppose the results instead gave 60 approval votes to
candidate Z, 61 to Y, and 55 to X. The final two voters in this case
would want to elect candidate Z by not voting for Y. But only in
imaginary elections can we know the results in advance. Without that
advance information, supporters of candidate Z are in a quandary-as,
in fact, are supporters of other candidates. IRV's alleged
mathematical deficiencies, on the other hand, have almost no
strategic impact because they depend on voters making complex
calculations with advance knowledge of election results"
3. Here is how AV can allow a candidate with strong
majority support to lose in an election with 100 voters. Under
plurality voting, Candidate A is the favorite choice of 65 voters,
candidate B is preferred by 25, and candidate C is the top choice of
only 10. Candidate A is the unambiguous winner, and C is a distant
third. Under AV, however, many voters might pick C as a weak, but
tolerable alternative. The final count might give 70 approval votes
to A, 35 votes to B, and 75 votes to C. Candidate C would
win. |
