Electoral threshold
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The electoral threshold, or election threshold, is the minimum share of votes that a candidate or political party requires before they become entitled to representation or additional seats in a legislature. This threshold is set in different ways in different situations. For example, in some party-list proportional representation systems, an electoral threshold requires that a party must receive a specified minimum percentage of votes (e.g. 5%), either nationally or in a particular electoral district, to obtain seats in the legislature. In single transferable voting, the quota acts as an electoral threshold to some degree, and it is possible to achieve it by receiving first-choice votes alone or by a combination of first-choice votes and votes transferred from other candidates based on lesser preferences. It is also a common occurrence in STV to see someone elected with less than the quota.
In some mixed-member proportional (MMP) systems, the election threshold determines which parties are eligible for top-up seats in the legislative chamber. Some MMP systems still allow a party to retain the seats they won in electoral districts even when they did not meet the threshold nationally. In some of these systems, top-up seats are allocated to a party that has not achieved the electoral threshold if it won at least one district seat or met some other minimum qualification.
Electoral thresholds can deny representation to small parties or force them into coalitions (joint slates). Such restraint is intended to make the elected government more stable by reducing party fragmentation and by keeping out fringe parties. Proponents of a high electoral threshold say that having seats in a legislature boosts the profile of a less popular party that does not deserve it, and that providing representation and possibly veto power to a party that receives only 1 percent of the vote is not appropriate. However, others argue that in the absence of a ranked ballot or proportional voting system at the district level, supporters of minor parties, barred from top-up seats, are effectively disenfranchised and denied the right to be represented by someone of their choosing.
Two boundaries can be defined. A threshold of representation (or threshold of inclusion) is the minimum vote share that might yield a party a seat under the most favourable circumstances for the party. The threshold of exclusion is the maximum vote share that could be insufficient to yield a seat under the least favourable circumstances. A third amount, the informal threshold, was calculated by Arend Lijphart as the mean of the two boundaries. Michael Gallagher gave this value the name effective threshold and set it at an amount of first preference votes equal to 75 percent of the Droop quota. However, he warned that this was to be used at the district level and not to assume that a party with a certain share of the overall vote was sure to have representation.
The electoral threshold is a barrier to entry for political parties to the political competition. Sometimes an electoral threshold is imposed district by district. Where the district magnitude (DM), the number of seats in a district, is high enough to allow less-popular parties to have representation and this is not desired, a district electoral threshold may be imposed just in those high-DM districts. In addition to the legislated electoral threshold, a natural threshold arises in fair voting systems from the district magnitude. The more seats, the smaller the percentage of district votes required to be elected.