Proportional Representation - Partial Proportionality

Partial Proportionality

Some nations with proportional elections, like Israel and the Netherlands, have one electoral district only: the entire nation, and the entire pie is cut up according to the entire outcome. Most nations have district systems in place where more than one person is elected per district. The constituency or district magnitude (DM) of a system is therefore measured by the number of seats per constituency. The greater the number of seats in a constituency, the more proportional the outcome will be. PR applied to a single-member district (SMD) is by necessity majoritarian. If the constituency is in a jurisdiction using list PR in its multimember districts (MMDs) the winning candidate needs a relative majority of the votes to win, so that the election in the SMD is by first-past-the-post. If the constituency is in a jurisdiction using PR-STV in its MMDs, an absolute majority of 50% plus 1 will likely be the minimum required for victory (depending on which quota is used) so that the election in the SMD is by the alternative vote. Four elected officials per district delivers a threshold of 20% (1/M+1) to gain a single seat. However, constituency borders can still be gerrymandered to reduce proportionality. This may be achieved by creating "majority-minority" constituencies - constituencies in which the majority is formed by a group of voters that are in the minority at a higher level. Proportional representation with the entire nation electing the single body cannot be gerrymandered.

Multimember districts do not necessarily ensure that an electoral system will be proportional. The bloc vote can result in "super-majoritarian" results in which geographical variations can create majority-minority districts that become subsumed into the larger districts. Also, a party that does not run enough people to fill all the seats it wins may be given those unfilled seats. This is termed an underhang.

Some nations, with either exclusively proportional representation or—as is the case with Germany—additional member systems, require a party list to achieve an election threshold—a set minimum percentage of votes to receive any seats. Typically, this lower limit is between two and five percent of the number of votes cast. Parties who do not reach that support are not represented in parliament, making majorities, coalitions and thus governments easier to achieve. Proponents of election thresholds argue that they discourage fragmentation, disproportionate power, or extremist parties. Opponents of thresholds argue that they unfairly redirect support from minor parties, giving parties which cross the threshold disproportionate numbers of seats and creating the possibility that a party or coalition will assume control of the legislature without gaining a majority of votes.

The most common way of measuring proportionality is the Gallagher Index.