Editing Mixed-member proportional representation (section)

== Procedures ==
[[File:German Federal Election 2021 - Results by Constituency & Regional Seats.svg|250px|thumb|right|Results of the [[2021 German federal election]]. The image shows both the seats directly won by constituency representatives and those gained via party lists. For example, the FDP (yellow) did not win a single constituency; all its 92 MPs were elected on party lists.]]
[[File:Bundestagswahl 05 stimmzett.jpg|200px|thumb|right|Ballot for [[Würzburg (electoral district)|electoral district 252, Würzburg]], for the [[2005 German federal election]]. Constituency vote on left, party list vote on right.]]In MMP, the voter casts two votes: one for a constituency representative and one for a party. In the [[Mixed single vote#Proportional systems|original variant]] used in Germany, citizens gave only one vote, so that voting for a representative automatically meant also voting for the representative's party, which is still used in some MMP elections today and is more robust against tactical voting than typical two-vote versions. Most of Germany changed to the two-vote variant to make local members of parliament (MPs) more personally accountable. Voters can thus vote for the local person they prefer for local MP without regard for party affiliation, since the partisan make-up of the legislature is determined only by the party vote. In the [[2017 New Zealand general election|2017 New Zealand election]], 27.33% of voters split their vote (voted for a local candidate of a different party than their party vote) compared to 31.64% in 2014.<ref>{{cite web|url=http://www.electionresults.govt.nz/electionresults_2017/statistics/split-votes-index.html|title=2017 Split Voting Statistics|website=electionresults.govt.nz}}</ref>

In each constituency, the representative is by default chosen using a [[Voting system#Single-winner methods|single winner method]] (though this is not strictly necessary), typically [[First-past-the-post voting|first-past-the-post]]: that is, the candidate with the most votes (plurality) wins.

Most systems used [[closed list|closed party lists]] to elect the non-constituency MPs (also called list MPs). In most jurisdictions, candidates may stand for both a constituency and on a party list (referred to in New Zealand as ''dual candidacy''). In Wales between 2006 and 2014 dual candidacy was banned, i.e. candidates were restricted to contend either for a constituency or for a party list, but not both. If a candidate is on the party list, but wins a constituency seat, they do not receive two seats; they are instead crossed off the party list and the party seat goes to the next candidate down.

In [[Bavaria]], the second vote is not simply for the party but for one of the candidates on the party's regional list: Bavaria uses seven regions for this purpose. A regional [[open list|open-list]] method was recommended for the [[United Kingdom]] by the [[Jenkins Commission (UK)|Jenkins Commission]] (where it is known as AMS) and for Canada by the [[Law Commission of Canada]]; neither recommendation was ever implemented.

In contrast, the [[open list|open-list]] method of MMP was chosen in November 2016 by voters in the [[2016 Prince Edward Island electoral reform referendum]].

In [[Baden-Württemberg]], there were no closed lists prior to 2022; they used the "best near-winner" method in a four-region model, where the regional members are the local candidates of the under-represented party in that region who received the most votes in their local constituency without being elected in it ([[Zweitmandat]], literally "second mandate").

=== Apportionment methods===
{{see also|Party-list proportional representation}}

At the regional or national level (i.e. above the constituency level) several different calculation methods have been used, but the basic characteristic of the MMP is that the '''total''' number of seats in the assembly, including the single-member seats and not only the party-list ones, are allocated to parties proportionally to the number of votes the party received in the party portion of the ballot. This can be done by different [[Apportionment (politics)|apportionment method]]s: such as the [[D'Hondt method]] or the [[Sainte-Laguë method]]. Subtracted from each party's allocation is the number of constituency seats that party won, so that the additional seats are compensatory (top-up).

===Dealing with overhang seats===
{{see also|Overhang seat}}
If a party wins more FPTP district seats than the proportional quota received by the party-list vote, these surplus seats are called [[overhang seat]]s ({{Lang|de|Überhangmandate}} in German), which may be an obstacle to achieving proportionality.

When a party wins more constituency seats than it would be entitled to from its proportion of (party list) votes, most systems allow for these [[overhang seat]]s to be kept by those candidates who earned it in the constituency elections. 

A counter-example is the ''[[Bundestag]]'' in Germany, where constituency winners may not always keep their seats in accordance with the latest modification of Germany's electoral law. 

In the MMP variant used in Romania in the [[2008 Romanian legislative election|2008]] and [[2012 Romanian legislative election|2012 legislative elections]], constituency seats were only earned by the leading candidate if the candidate also achieved an absolute majority of votes in their district, thereby preventing overhang seats.

In [[New Zealand House of Representatives]], all members elected for constituencies keep their seats. For example, in the [[2008 New Zealand general election]] the [[Māori Party]] won 2.4% of the party vote, which entitled it to 3 seats in the House but won 5 constituency seats, leaving an overhang of 2 seats. This was compensated for giving two additional seats to other parties, which resulted in a 122-member house. If the constituency seats won had been in proportion to the party vote for the Māori Party, there would have been a normal 120-member house.

To combat disproportionalities caused by overhang seats in most German states, [[leveling seats]] (''Ausgleichsmandate'' in German) are added to compensate for overhang seats and thereby achieve proportionality. Usually 50 percent of total seats are compensatory seats, but that proportion varies. For example, in the provincial parliament (''[[Landtag]]'') of North Rhine Westphalia, 29% of the seats are levelling seats, which compensate for difference between district results based on local votes and the party's share of the party vote. More may be added to balance overhangs. If a party wins more local seats than its proportion of the total party vote justifies, the size of the ''Landtag'' increases so that the total outcome is proportional to the party votes, with other parties receiving additional list seats to achieve proportionality. The leveling seats are added to the normal number of seats for the duration of the electoral period. In the German state of [[Bavaria]], the constituency votes and party votes are combined to determine the proportional allocation of seats.

[[Scottish Parliament|Scotland]] uses a modified variant of MMP known as the [[Additional Member System (UK)|additional member system]] where due to the nature of the calculations used to distribute the regional list seats, overhang seats are not possible; the list allocation works like a [[Mixed-member majoritarian representation|mixed-member majoritarian]] system, but in using the [[d'Hondt method]]'s divisors to find the averages for the allocation, the first divisor for each party takes into account the number of constituency seats won by the party. Wales is similar.) 

For example, a party that won 7 constituency seats would start with a divisor of 8 (7 seats + 1 per the method's divisor formula) instead of 1. The resulting table would then give 7 seats for Scotland (and 4 seats for Wales) to the parties possessing the highest averages on the table, (Neither devolved parliament uses a table, instead using a sequential method.) MMP's compensatory effect is in the fact that a party that won constituency seats would have lower averages on the table than it would if the election used mixed-member majoritarian. Because there is no provision for overhang seats, there have been cases in Scotland where a party ended up with more seats and others with fewer total seats than their proportional entitlement. This occurred, for example, in the [[South Wales East (Senedd Cymru electoral region)|South East Wales electoral region]] in 2007 and 2016. In 2007 [[Welsh Conservatives]] were under-represented while Independents got one more seat than they were due. In 2016 in that same electoral region, [[Welsh Labour]] was over-represented, while [[Plaid Cymru]] was under-represented. 

Welsh Labour has also been over-represented on this basis in every election in the [[South Wales West (Senedd Cymru electoral region)|South Wales West]] region, and every election in the [[South Wales Central (Senedd Cymru electoral region)|South Wales Central]] region, apart from the 2003 election. This situation arose because Labour held an overwhelming majority of constituency seats in these regions, more than its due share proportionally. Only around one-third of the total number of seats are top-up, in the form of additional regional seats, so that is insufficient to fully compensate for Welsh Labor's over-representation
{| class="wikitable"
! colspan="4" rowspan="3" |
! colspan="2" rowspan="2" |[[Parallel voting]]
([[Mixed-member majoritarian representation|MMM]])
! colspan="6" |Broadly mixed-member proportional type of system (MMP)
|-
! colspan="2" |Additional member system (AMS)
! colspan="2" |Overhang seats re-added
! colspan="2" |True MMP (with leveling seats)
|-
| colspan="2" |[[File:AMS_example_parallel_total_seats.svg|frameless]]
| colspan="2" |[[File:AMS_total_seats.svg|frameless]]
| colspan="2" |[[File:AMS_example_MMP_overhang_only_total_seats.svg|frameless]]
| colspan="2" |[[File:AMS_example_MMP_total_seats.svg|frameless]]
|-
! colspan="2" |Party
!Popular vote (%)
!Constitu&shy;encies won
!Seats
!Share (%)
!Seats
!Share (%)
!Seats
!Share (%)
!Seats
!Share (%)
|-
| style="background:#D10000" |
|Party A
|43%
|54
|67 (54+13)
|67%
|54 (54+0)
|54%
|54 (54+0+0)
|48%
|71 (54+0+17)
|43%
|-
| style="background:#0008A5" |
|Party B
|41%
|11
|24 (11+13)
|24%
|34 (11+23)
|34%
|41 (11+23+7)
|36%
|68 (11+23+34)
|41%
|-
| style="background:#03AA00" |
|Party C
|13%
|0
|3 (0+3)
|3%
|7 (0+7)
|7%
|13 (0+7+6)
|12%
|21 (0+7+14)
|13%
|-
| style="background:#820084" |
|Party D
|3%
|5
|5 (5+0)
|5%
|5 (5+0)
|5%
|5 (5+0+0)
|4%
|5 (5+0+0)
|3%
|-
|
|TOTAL
|100%
|70
|100 (70+30)
|100%
|100 (70+30)
|100%
|113 (70+30+13)
|100%
|165 (70+30+65)
|100%
|-
| colspan="4" |Index of disproportionality
([[Gallagher index|Gallagher]])
| colspan="2" |22.01 (disproportional)
| colspan="2" |10.25 (moderately disproportional)
| colspan="2" |4.97 (considered proportional)
| colspan="2" |0.25 (highly proportional)
|-
| colspan="4" |'''Method used'''
| colspan="2" |Independent PR tier
| colspan="2" |Fixed number of compensatory seats
| colspan="2" |Number of (extra) leveling seats =
number of overhang seats
| colspan="2" |As many leveling seats as needed
|-
| colspan="4" |'''This type of system used in'''
| colspan="2" |Russia, among others
| colspan="2" |Scotland, among others
| colspan="2" |New Zealand, Germany (until 2009)
| colspan="2" |Germany (2013, 2017)
|}

===Threshold===
{{see also|Election threshold}}
As in numerous [[party-list|proportional systems]], in many MMP systems, in order to be eligible for list seats, a party must earn at least a certain percentage of the party vote, or no candidates will be elected from the party list. Candidates having won a constituency will still have won their seat. In New Zealand the threshold is 5% and in Bolivia 3%. 

in Germany the threshold is 5% for elections for federal parliament and most state parliaments. And under recent changes to Germany's election law, the constituency seat may be taken away from the party. 

A party that does not achieve the threshold can also be eligible for list seats if it wins at least three constituency seats in Germany, or at least one in New Zealand. Having a member with a 'safe' constituency seat is therefore a tremendous asset to a [[minor party]] in New Zealand.

In elections for the Scottish Parliament, no threshold is set. The [[district magnitude]] of each electoral region is small enough to impose an inherent threshold in the seat distribution calculations. In 2021, with regional DM of 16, the effective threshold was about 7 percent of the region's votes, or about 17,000 to 20,000 votes of the total 2.7 million valid votes cast, but each region is discrete from the other regions so if a party is spread across multiple regions, it may not win even one seat even if it has more than 40,000 votes in total. Such happened to the [[Alba Party]] in 2021.

=== By-elections and replacement of list representatives ===
{{see also|By-election}}