Correcting the Spoiler Effect
Since plurality races with three or more candidates allow a winner to be elected with less than 50% of the vote, two like-minded candidates can split their base of support, allowing a less desired candidate to win. This is known as the "spoiler effect." This winning candidate, if elected with less than 50% of votes, does not necessarily have the support of most voters and may in fact represent views in conflict with the majority of voters. In some instances, vote-splitting between two candidates can lead to the election of a candidate whose views are the polar opposite of the majority of voters.
In response to the spoiler effect, candidates face an incentive to engage in negative campaigning against those who hold views similar to their own and who threaten to cut into their base of support. This can in turn drive voter turnout down and draw attention away from serious policy concerns in a campaign.
With the advent of modern polling techniques, some candidates are seen throughout their candidacies as "a lost cause" if their numbers aren't very strong. Polling information is likely to make voters second-guess their support for these candidates. Thus, they find themselves inclined to vote for a "viable" candidate who may not reflect their values as well as other candidates might, a "lesser of two evils." This incentive for voters to engage in strategic voting is also a side effect inherent in plurality elections.
If these calculations reveal a candidacy to not be very viable, candidates who represent small but legitimate viewpoints that deserve a seat at the table can often be marginalized and discouraged from running for office. This weakens the range of options voters have in elections, while contributing to declining voter turnout and discussion of issues of importance to voters.
Consequently, this way of thinking often helps entrench the two major political parties and keeps minor parties and independent candidates from attracting new pools of voters or bringing new ideas or issues into the public debate. Indeed, the spoiler effect has a tremendous impact on the complexion of our government and party system.
The only way to solve this problem is to ensure the winner emerges with a "spoiler-free" majority.
Because instant runoff voting (IRV) is designed to secure a majority victory, it assures that the so-called "spoiler effect" will not result in undemocratic outcomes. IRV affords voters more choices and promotes broader participation by accommodating multiple candidates in single seat races. Voters may support their favorite candidate without fear of splitting a base of support or swinging the election to their least favorite candidate. Thus it solves the problem of choosing between the "lesser of two evils" and encourages greater participation from voters and candidates, while fostering cooperative campaigns built on a more robust discussion of issues.