Spoiler effect

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The "spoiler effect" is a term to describe the effect a minor party candidate with little chance of winning can have on a close election, in which their candidacy results in the election being won by a candidate dissimilar to them rather than a candidate similar to them by taking votes away from the viable candidate with similar views. The minor candidate is often referred to as a "spoiler." It is a real life demonstration of the kingmaker scenario.

The "spoiler effect" is one of the components contributing to the effect known as Duverger's law, which states that the first-past-the-post election system creates and preserves a two-party system. A voting system known as preferential voting, can lessen this effect. In a preferential voting system, a voter can vote for a minor party candidate as their first choice, and in addition, they can record a preference between the remaining candidates, whether they are in a "major party" or not. For example, voters for a very liberal candidate might select a somewhat liberal candidate as their second choice, thus minimising the chances that their vote will result in the election of a conservative candidate. Approval voting can also reduce the impact of the "spoiler effect".

In sports, the 'spoiler effect' refers to a similar phenomenon, in which a team has failed to win enough games to make the playoffs, but affects the playoffs anyway by beating a more successful team before the end of the season.

[edit] Vote splitting

Main article: Vote splitting

"Vote splitting" is a phenomenon related to the "spoiler effect." Vote splitting is the distribution of votes among otherwise viable similar candidates in a situation that decreases the likelihood of winning for any of the similar candidates. This effect was observed in 1987, when Roh Tae-woo won the South Korean presidential election with just under 36% of the popular vote after his two main rivals split the vote.

As an example of vote splitting, if 30 percent of voters prefer candidate A, another 30 percent prefer a similar candidate B, and the remaining 40 percent prefer a dissimilar candidate C, then plurality voting identifies candidate C as the winner, even though a majority of voters (60 percent) prefer either candidate A or candidate B.

Voting methods that are vulnerable to strategic nomination, especially methods that fail independence of clones, are vulnerable to vote splitting. Vote splitting also can occur in situations that do not involve strategic nomination, such as talent contests (such as American Idol) where earlier rounds of voting determine the current contestants. In the United States vote splitting commonly occurs in primary elections.^[1] One could say that the function of a primary election is to get all vote splitting (within a party) out of the way, so that it does not effect the secondary election. However, since primary elections only occur within each party, vote splitting can still occur between parties in the secondary election.

Plurality voting is especially vulnerable to vote splitting. Runoff voting methods are less vulnerable, and pairwise-counting Condorcet methods minimize vote splitting effects.^[1]

In addition to applying to single-winner voting systems (such as used in the United Kingdom, the United States and Canada), a split vote can occur in proportional representation methods that use election thresholds, such as in Germany and Turkey. In these cases, "fringe" parties that do not meet the threshold can take away votes from larger parties with similar ideologies.

[edit] Mathematical definitions

Possible mathematical definitions for the spoiler effect include failure of independence of irrelevant alternatives (IIA) and vote splitting.

Arrow's impossibility theorem shows that rank-voting systems are unable to satisfy the independence of irrelevant alternatives criterion without exhibiting other undesirable properties as a consequence. However, different voting systems are affected to a greater or lesser extent by IIA failure. For example, instant runoff voting is considered to have less frequent IIA failure than First Past the Post. The local independence of irrelevant alternatives criterion is similar to IIA, but which can be passed by some ranked ballot methods.

[edit] The spoiler effect in American presidential elections

One often cited example of the "spoiler effect" at work was the 2000 U.S. Presidential election. In that election, George W. Bush and Al Gore had a very close election in many states, with neither candidate winning a majority of the votes. In the state of Florida, the final certified vote totals show that Bush won just 537 more votes than Gore, thus winning the state. Since the Florida votes were among the last to be reported, and because the results were so close, and there was a vote recount, some say that the Florida result "decided the election". Some Gore supporters believed that many of the 97,421 votes that went to Ralph Nader in that state would likely have been votes for Gore, had Nader not been running in the election. Some Gore supporters contend that Nader's candidacy "spoiled" the election for Gore by taking away enough votes from Gore in Florida and many other states (in particular, New Hampshire being the allegation most statistically supportable) to allow Bush to win. Their argument is bolstered by a poll of Nader voters, asking them for whom they would have voted had Nader not run, which said 45 percent of them would have voted for Mr. Gore, 27 percent would have voted for Mr. Bush, and the rest would not have voted^[2]. Nader supporters say he was running, in part, to protest the positions of Bush and Gore. Ralph Nader, defending himself claimed "Defeat is a powerful motivator that democracy allows and encourages. Had Nader not been on the ballot, pro-Bush or anti-Gore voters might have voted for Bush". Nader himself and many of his supporters argue that most Nader voters would have chosen another minor party candidate, or abstained from voting, had he not been on the ballot. Some observers began to refer to this as the 'Nader effect' after the 2000 election. Other observers note that this phenomenon existed long before Nader.

These are third-party candidates who have been accused of denying victory to a major nominee.

• Charles Cotesworth Pinckney, 1800
• James Birney, 1844
• Martin van Buren, 1848
• Theodore Roosevelt, 1912
• George Wallace, 1968
• Ross Perot, 1992
• Ralph Nader, 2000

The spoiler effect also sometimes occurs in congressional elections and elections for state offices.

[edit] References

[edit] See also

• The Decoy effect is related, but suggests (for example) that, in 2000, the presence of Nader pulled votes from Bush to Gore, by making Gore appear more moderate by comparison.
• Strategic nomination