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Droop quota (formula)

In counting votes for electing candidates under a single transferable vote electoral system, the minimum number of votes needed for a candidate to be elected (the quota) can be calculated by using the Droop quota formula.  The quota is calculated as follows: first, the total valid vote in the electoral district is divided by one plus the number of members to be elected; then, one is added to the total (fractions are ignored).

 The Droop quota is the smallest number of votes to elect enough candidates to fill all the seats being contested in an electoral district, while being just big enough to prevent any more being elected.  If the Droop formula is applied to a single member district, the quota is the total votes (100 percent) divided by 1 plus the number of members to be elected (1); the result is 100 divided by 2 which gives 50 percent plus one vote—a share of the vote that only one candidate can get.

 H R Droop was an English lawyer who suggested this formula in 1868 as a component of an electoral system.
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