Open lists

Open list describes any variant of party-list proportional representation where voters have at least some influence on the order in which a party's candidates are elected. This as opposed to closed list, which allows only active members, party officials, or consultants to determine the order of its candidates and gives the general voter no influence at all on the position of the candidates placed on the party list. Additionally, an open list system allows voters to select individuals rather than parties. Different systems give voter different amounts of influence. Voter's choice is usually called preference vote.

A "relatively closed" open list system is one where a candidate must get a full quota of votes on his or her own to be assured of winning a seat. (This quota, broadly speaking, is the total number of votes cast divided by the number of places to be filled. Usually the precise number required is the Hare quota, but the Droop quota can also be used.) The total number of seats won by the party minus the number of its candidates that achieved this quota gives the number of unfilled seats. These are then successively allocated to the party's not-yet-elected candidates who were ranked highest on the original list.

In a 'more open' list system, the quota for election could be lowered from the above amount. It is then (theoretically) possible that more of a party's candidates achieve this quota than the total seats won by the party. It should therefore be made clear in advance whether list ranking or absolute votes take precedence in that case.

In Dutch elections (for example to the House of the Representatives) the voter can give his vote to any candidate in a list; the vote for this candidate is called a "preference vote" (voorkeurstem in Dutch). If a candidate has at least 25% of the quota then he/she takes priority over the party's other candidates who stand higher on the party list but received fewer preference votes.

An example: A party list got 5000 votes. If the quota is 1000 votes, then the party wins five seats.

Candidates #1, #7 and #4 have each achieved 25% of the quota (250 preference votes or more). They get the first three of the five seats the party has won. The other two seats will be taken by #2 and #3, the two highest remaining positions on the party list. This means that #5 is not elected even though being the fifth on the list and having more preference votes than #2. In practice, at the national level only one or two candidates can precede on their lists. This happens more often at the local level where the quota (in absolute numbers of votes) is lower. Parties usually allow candidates to ask for preference votes, but without campaigning negatively against other candidates on the list.

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Wikipedia