It can also be used in multiple member constituency elections.
Many of the mathematical criteria by which voting methods are compared were formulated for voters with ordinal preferences. If voters vote according to the same ordinal preferences in both rounds, criteria can be applied to two-round systems of runoffs, and in that case, each of the criteria failed by IRV is also failed by the two-round system as they relate to automatic elimination of trailing candidates.
Partial results exist for other models of voter behavior in the two-round method: Satisfied Criteria[ edit ] Condorcet loser criterion The Condorcet loser criterion states that "if a candidate would lose a head-to-head competition against every other candidate, then that candidate must not win the overall election".
Independence of clones criterion The independence of clones criterion states that "the election outcome remains the same even if an identical candidate who is equally preferred decides to run.
Majority criterion The majority criterion states that "if one candidate is preferred by an absolute majority of voters, then that candidate must win". Mutual majority criterion The mutual majority criterion states that "if an absolute majority of voters prefer every member of a group of candidates to every candidate not in that group, then one of the preferred group must win".
Resolvability criterion The resolvability criterion states that "the probability of an exact tie must diminish as more votes are cast". Non-satisfied Criteria[ edit ] Condorcet winner criterion The Condorcet winner criterion states that "if a candidate would win a head-to-head competition against every other candidate, then that candidate must win the overall election".
It is incompatible with the later-no-harm criterion, so IRV does not meet this criterion.
IRV is more likely to elect the Condorcet winner than plurality voting and traditional runoff elections. The California cities of Oakland, San Francisco and San Leandro in provide an example; there were a total of four elections in which the plurality-voting leader in first-choice rankings was defeated, and in each case the IRV winner was the Condorcet winner, including a San Francisco election in which the IRV winner was in third place in first choice rankings.
IRV, like all preferential voting methods which are not positionaldoes not meet this criterion. Independence of irrelevant alternatives criterion The independence of irrelevant alternatives criterion states that "the election outcome remains the same even if a candidate who cannot win decides to run.
IRV does not meet this criterion: A chart in the article on the Schulze method compares various ranked ballot methods. Comparison to first-past-the-post[ edit ] At the Australian federal election in Septemberout of the House of Representatives seats or 90 percent were won by the candidate who led on first preferences.
The other 15 seats 10 percent were won by the candidate who placed second on first preferences. This implies that IRV is susceptible to tactical voting in some circumstances. Research concludes that IRV is one of the less-manipulable voting methods, with theorist Nicolaus Tideman noting that, "alternative vote is quite resistant to strategy"  and Australian political analyst Antony Green dismissing suggestions of tactical voting.
The change in lower candidates is important: Tactical voting in IRV seeks to alter the order of eliminations in early rounds, to ensure that the original winner is challenged by a stronger opponent in the final round.
For example, in a three-party election where voters for both the left and right prefer the centrist candidate to stop the "enemy" candidate winning, those voters who care more about defeating the "enemy" than electing their own candidate may cast a tactical first preference vote for the centrist candidate.
The mayoral election in Burlington, Vermont provides an example in which strategy theoretically could have worked but would have been unlikely in practice.
In that election, most supporters of the candidate who came in second a Republican who led in first choices preferred the Condorcet winner, a Democrat, to the IRV winner, the Progressive Party nominee.
Yet because the Republican led in first choices and only narrowly lost the final instant runoff, his backers would have been highly unlikely to pursue such a strategy. Spoiler effect The spoiler effect is when a difference is made to the anticipated outcome of an election due to the presence on the ballot paper of a candidate who predictably will lose.
Most often this is when two or more politically similar candidates divide the vote for the more popular end of the political spectrum.AV is fairer than first past the post. This is not quite so clear-cut. The AV system is a different system and, The Independent believes, a better one.
. You are here People. Political Science staff – Phone numbers: please place prefix + before the extension number; Email addresses: please add @kaja-net.com after email address below. Learn how to design large-scale systems.
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It is relatively easy for a voter to understand how the largest remainder method allocates seats.
The Hare quota gives an advantage to smaller parties while the Droop quota favours larger parties. However, whether a list gets an extra seat or not may well depend on how the remaining votes are distributed among other parties: it is quite .
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