Multiwinner voting

Multiwinner voting, also called multiple-winner elections or committee voting or committee elections, is an electoral system in which 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. There are many scenarios in which multiwinner voting is useful. They can be broadly classified into three classes, based on the main objective in electing the committee: Excellence. Here, each voter is an expert, and each vote expresses his/her opinion about which candidate/s is "better" for a certain task. The goal is to find the "best" candidates. An example application is shortlisting: selecting, from a list of candidate employees, a small set of finalists, who will proceed to the final stage of evaluation (e.g. using an interview). Here, each candidate is evaluated independently of the other candidates. If two candidates are similar, then probably both will be elected (if they are both good), or both will be rejected (if both are bad). Diversity. Here, the elected candidates should be as different as possible. For example, suppose the candidates are possible locations for constructing a facility, such as a fire station. Most citizens naturally prefer a fire station in the city center. However, there is no need to have two fire-stations in the same place; it is better to diversify the selection and put the second station in a more remote location. In contrast to the "excellence" setting, if two candidates are similar, then probably exactly one of them will be elected. Another scenario in which diversity is important is when a search engine selects results for display, or when an airline selects movies for screening during a flight. Proportionality. Here, the elected candidates should represent in scientifically-balanced way the diverse opinion held by the population of voters, measured by the votes they cast, as much as possible.