Droop quota

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In the study of electoral systems, the Droop quota (sometimes called the Hagenbach-Bischoff, Britton, or Newland-Britton quota^[1][a]) is the minimum number of votes needed for a party or candidate to guarantee they will win at least one seat in a legislature.^[3][4]

The Droop quota generalizes the concept of a majority to multiwinner elections. Just as a candidate with a majority (any number exceeding half of all votes) is guaranteed to be declared winner in a one-on-one election, a candidate who holds more than one Droop quota's worth of votes at any point is guaranteed to win a seat in a multiwinner election.^[4]

Besides establishing winners, the Droop quota is used to define the number of excess votes, i.e. votes not needed by a candidate who has been declared elected. In proportional quota-rule systems such as STV or the expanding approvals rule, these excess votes can be transferred to other candidates, preventing them from being wasted.^[4]

The Droop quota was first suggested by the English lawyer and mathematician Henry Richmond Droop (1831–1884) as an alternative to the Hare quota.^[4]

Today, the Droop quota is used in almost all STV elections, including those in the Republic of Ireland, Northern Ireland, Malta, and Australia.^{[citation needed]} It is also used in South Africa to allocate seats by the largest remainder method.^[4]

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