Concept
Multiwinner approval voting, also called approval-based committee voting, is a multi-winner electoral system that uses approval ballots. Each voter may select ("approve") any number of candidates, and multiple candidates are elected. The number of elected candidates is usually fixed in advance. For example, it can be the number of seats in a country's parliament, or the required number of members in a committee. Multiwinner approval voting is an adaptation of approval voting to multiwinner elections. In a single-winner approval voting system, it is easy to determine the winner: it is the candidate approved by the largest number of voters. In multiwinner approval voting, there are many different ways to decide which candidates will be elected. The straightforward extension of approval balloting to multi-winner elections is called block approval voting and is a type of multiple non-transferable vote, where each voter can select an unlimited number of candidates, and the k candidates with the most approval votes win (where k is the predetermined committee size). This does not provide proportional representation and is subject to the Burr dilemma, among other problems. Limited block approval voting is a type of multiple non-transferable vote, in which the k candidates with the most votes win, and each voter can select a limited number of candidates, but that limit is more than k. This is subject to the same problems as unlimited block approval voting. Plurality block voting and Limited voting Plurality-at-large or plurality block voting (BV) and limited voting (LV) are both types of the multiple non-transferable vote category of multi-winner systems. Under plurality block voting, each voter has up to as many votes as there are seats to be filled, but no more than one per candidate and under limited voting, each voter has less votes than seats to be filled. Plurality block voting provides majoritarian representation, while limited voting is semi-proportional.
