Vote Splitting & The Spoiler Effect

Vote splitting is when similar candidates divide their support. It occurs in choose-one voting when there are more than two candidates in the race and in ranked-choice voting whenever you have three or more competitive candidates in a close race, but it never happens with approval voting.

Situation: Candidates A & B are similar in a lot of ways and are both liked by a majority of the population (54% & 53%). Candidate C is not liked by a majority of the population (46%). Candidate A should win in this situation. Now let’s see how different voting methods choose a winner.

Choose-One Voting

Outcome: Candidates A & B split 54% of the vote, 29% to 25%. Candidate C gets 46%, causing candidate C to win.

Spoiler Effect: People who favor A over B will see B as a spoiler candidate saying, “If only they would have voted for A instead of B, C wouldn’t have won and we would have a candidate more people like.” This causes people to not vote for candidates like B next time, even though they like B.

Ranked-Choice Voting

Outcome: Candidates A & B split the vote 29% to 25% in a close first round. Candidate C gets 46%, causing candidate B to be eliminated. When B’s votes are redistributed using second choices, most go to A (20%), but some go to C (5%) causing C to win with 51%, even though a majority of people would have preferred either A or B over C.

Spoiler Effect: People who favor A over B will see B as a spoiler candidate saying, “If only they would have put A first, C would have been eliminated first and we would have a candidate more people like.” This causes people to not rank candidates like B first next time, even though they like B more than A.

Approval Voting

Outcome: Candidates A & B get approved at a rate of 54% and 53%. Candidate C gets 46%, leading candidate A to win.

Spoiler Effect: The spoiler effect is eliminated here because all of the voter’s preferences are counted at once, leading to a candidate who is most liked winning. Allowing people who like candidates like B, to still choose B the next time around, while also choosing A, to ensure a lesser liked candidate, C, never wins. Because who knows, maybe B will have more support next time and win.