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Like virtually all other electoral systems, in the two-round system, there is potential for both tactical voting and strategic nomination.〔The Gibbard-Satterthwaite theorem shows that any voting method which does not allow tactical voting must be either dictatorial or non-deterministic (incorporating random elements). A non-deterministic system may not select the same outcome every time it is applied to the same set of ballots, so non-deterministic systems are rarely suggested for public elections.〕 Tactical voting is where voters do not vote in accordance with their true preferences, but instead vote insincerely in an attempt to influence the result. Runoff voting is intended as a method that reduces tactical voting, but two tactics called compromising and pushover are still possible in many circumstances. In particular voters are strongly encouraged to compromise by voting for one of the three leading candidates in the first round of an election. Strategic nomination is where candidates and political factions influence the result of an election by either nominating extra candidates or withdrawing a candidate who would otherwise have stood. Runoff is intended to reduce the spoiler effect, but it does not eliminate it. A famous example of the importance of both strategic nomination and tactical voting in runoff voting was the 2002 French presidential election. ==Sample election== For illustrative purposes, the following is a sample election that does not involve any tactical manipulation. Imagine an election to choose which food to eat for dessert. There are 100 people having dessert and three candidates: Ice Cream, Apple Pie and Fruit. Runoff voting is used to find the winner. Round 1: In the first round of voting each diner votes for the one candidate they most prefer. The results are as follows: *Ice Cream: 43 votes *Apple Pie: 16 votes *Fruit: 41 votes Round 2: No candidate has an absolute majority of votes (in this election that would be 51) so the two candidates with the most votes, Ice Cream and Fruit, proceed to a second round, while Apple Pie is eliminated. Because their favourite candidate has been eliminated Apple Pie supporters must now vote for one of the two remaining candidates. The Apple Pie supporters split into two even groups: 8 vote for Ice Cream and 8 for Fruit. Of those who supported Ice Cream and Fruit in the first round, no one decides to change their vote. The results of the second round are, therefore, as follows: *Ice Cream: 51 *Fruit: 49 Result: Ice Cream now has an absolute majority so is declared the winner. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tactical manipulation of runoff voting」の詳細全文を読む スポンサード リンク
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