Vote splitting

rdf:langString Vote splitting

rdf:langString Vote splitting is an electoral effect in which the distribution of votes among multiple similar candidates reduces the chance of winning for any of the similar candidates, and increases the chance of winning for a dissimilar candidate. Vote splitting most easily occurs in plurality voting (also called first-past-the-post) in which each voter indicates a single choice and the candidate with the most votes wins, even if the winner does not have majority support. For example, if candidate A1 receives 30% of the votes, similar candidate A2 receives another 30% of the votes, and dissimilar candidate B receives the remaining 40% of the votes, plurality voting declares candidate B as the winner, even though 60% of the voters prefer either candidate A1 or A2. Under such systems vote pairing (also called vote swapping, co-voting or peer to peer voting) can mitigate the effect, but it requires two voters in different districts to agree, and identifying probabilities of candidates winning in those districts. A vote swap effectively preserves the total support for each party but moved it to where it is most effective. It is legal and practiced in US, Canadian and especially UK elections. Pairwise-counting Condorcet methods minimize vote splitting effects. Cardinal voting methods are immune to vote splitting if it is assumed that voters rate candidates individually and independently of knowing the available alternatives in the election, using their own absolute scale, since each candidate is rated independently of each other. This assumption implies that some voters having meaningful preferences in an election with only two alternatives will necessarily cast a vote which has little or no voting power, or necessarily abstain. If it is assumed to be at least possible that any voter having preferences might not abstain, or vote their favorite and least favorite candidates at the top and bottom ratings respectively, then these systems are not immune to vote splitting. Plurality-runoff voting methods (like exhaustive ballot, two-round system/top-two primary, instant-runoff voting, supplementary vote, and contingent vote) still suffer from vote-splitting in each round, but can somewhat reduce its effects compared to single-round plurality voting. A well-known effect of vote splitting is the spoiler effect, in which a popular candidate loses an election by a small margin because a less-popular similar candidate attracts votes away from the popular candidate, allowing a dissimilar candidate to win. As a result, the notion of vote splitting is controversial because it can discourage third-party candidates. All voting systems have some degree of inherent susceptibility to strategic nomination considerations. Strategic nomination takes advantage of vote splitting to defeat a popular candidate by supporting another similar candidate. Vote splitting is one possible cause for an electoral system failing the independence of clones or independence of irrelevant alternatives fairness criteria.