The Single Transferable Vote (STV) system is a form of preferential voting which aims to achieve proportional representation in multiple-candidate elections (as for parliaments), and to mitigate against tactical spoiler effects in single candidate elections (as for constituencies). Instant Runoff Voting, also known as the Hare system, Alternative Vote, or the Clark system, is a variant of STV. In an STV system, voters cast a single vote but rank candidates or parties in order of preference. Their votes may then be reassigned based on whether or not their first preference achieves a certain quota of votes.