Overhang seat

Under MMP, a party is entitled to a number of seats based on its share of the total vote. If a party's share entitles it to ten seats and its candidates win seven constituencies, it will be awarded three list seats, bringing it up to its required number. This only works, however, if the party's seat entitlement is not less than the number of constituencies it has won. If, for example, a party is entitled to five seats, but wins six constituencies, the sixth constituency seat is referred to as an overhang seat. Overhang can result from an unproportional distribution of constituencies as well as strong region-based support or the existence of regional parties.[2]

The two mechanisms that together increase the number of overhang seats are:[3]

1. winning many constituencies;
2. decreasing the number of party votes and therefore the number of seats to which the party is proportionally entitled.

In many countries, overhang seats are rare – a party that is able to win constituency seats is generally able to win a significant portion of the party vote as well. There are, however, some circumstances in which overhang seats may arise relatively easily:

• Few major parties, large number of minor parties – When there are only one or two major parties, but a relatively large number of minor parties that, combined, achieve a significant share of the total proportional vote, but fail to elect any constituency seats, the large parties often end up with overhang seats.
• Similar lead across constituencies – If one party wins all or most constituencies of a relevant area with a rather low margin, it would be more prone to overhang mandates than if different parties lead in different constituencies, with the same overall share of each of the parties. As such, if there is less difference between constituencies, overhang seats are more probable.
• A large number of constituencies compared with the total number of seats – If too many seats are used for constituencies, the remainder are less likely to ensure strict proportionality.
• Unevenly sized constituencies – Candidates that win small constituencies by a narrow margin do not generate enough votes to justify their full seats under a proportional system.
• Low turnout in some constituencies – This has the same effect as small constituencies. Furthermore, turnout and party preferences may be highly correlated, e.g. rural vs. urban areas.
• Small number of seats to be allocated – The higher the absolute number of constituencies, the more likely it is that different reasons for overhang seats will balance out between parties. E.g., after the German federal Bundestag election in 2013, the main reason for overhang seats was that some compensation happens for party's state lists instead of at the federal level only.
• Individual candidates with strong local followings – Sometimes, a particular politician will have strong support in their own constituency, but will belong to a party with very low support, even in their own area. The candidate will be elected based on their own qualities, but the party they belong to will not receive enough votes to justify the candidate's seat. In the case of independent candidates, this is usually guaranteed – they have no party at all, and so obviously cannot win votes under MMP's party-list proportional representation. However, some countries, such as New Zealand, have special rules dealing with independents – seats won by these candidates are exempted from the proportional system altogether.
• Regional parties – Parties based in a particular region may win a substantial number of constituency seats in that region without necessarily gaining a large share of the national vote. Parties focused on particular ethnic or religious minorities may also come under this category, particularly if seats are reserved for these groups.
• Tactical voting – Voters in countries that can cast a vote in the list vote and cast a local vote (such as Germany) may decide not to vote for a local candidate that has little chance of winning but still support that party on the list vote. Parties that win many local seats but attract a reduced list vote may receive an overhang as a result.
• Decoy parties – Party labels in the constituencies can be deliberately mismatched with those in the proportional vote in an attempt to induce tactical voting. In Italy in 2001, two lists won a significant majority of the total number of first-past-the post seats, despite winning almost none of the proportional vote. The system, nicknamed scorporo, was not a type of additional member system in which overhangs could occur, it resulted in a significant distortion to the desired compensatory nature.

Overhang seats are dealt with in different ways by different systems.

Prior to German reunification overhang mandates - particularly at the federal level - were relatively rare and never amounted to more than five (out of over 400 total seats) in any given Bundestag and several federal elections resulted in no overhang at all.[5] This was in part due to the relative strength of the two "Volksparteien" CDU/CSU and SPD which combined to over 60% and sometimes over 80% of the federal vote and as only half as many constituencies as seats exist, it was unlikely for a party to win more than a handful more constituencies in any given state than their vote-share would have given them in list seats.[6][7]

However, this began to change as East Germany started participating in German federal elections starting with the 1990 German federal election. As the election results notably differ in East and West[8][9] Particularly as the PDS (later fused and renamed to Die Linke) achieved far better election results in the East where it approached "Volkspartei" status.[10][11][12][13] Thus constituencies which had previously been won by absolute majorities or at least a large plurality could now be won by slimmer pluralities than in previous elections. For example, the SPD while sweeping all 6 constituencies in Mecklenburg Vorpommern in the 2021 German federal elections achieved "only" 29.1% of the statewide de:Zweitstimmen. In the 1994 German federal election the re-elected Kohl government supported by a "black-yellow" coalition (CDU/CSU and FDP) achieved a relatively slim majority of 341 out of 672 seats to the opposition's (SPD, Alliance 90/The Greens, PDS) 331 seats at the opening session. This majority would've been even narrower if not for twelve overhang mandates the CDU/CSU had achieved, which were however partially mitigated by the four overhang mandates for the opposition SPD.[14] This led to much more public debate on the existence of overhang mandates and what to do about them.[15][16][17][18] There was even a challenge of the validity of the election result based on the overhang seat issue raised by a private citizen after the 1994 election, which was however dismissed as "obviously without merit" ("offensichtlich unbegründet").[19]

The problem thus turning from a theoretical consideration to a real issue, the German Constitutional Court as early as 1997 ruled that a "substantial number" of overhang mandates which weren't equalized through leveling seats were unconstitutional.[20] The issue became more pressing as negative vote weight was introduced as a phenomenon to a broader public due to the 2005 German federal election in the constituency Dresden I having to be held later than the election in the other 298 constituencies after a candidate in the constituency died days ahead of the election date. Der Spiegel published an article between the main election and the makeup election in Dresden I lining out how more votes for the CDU could lead to them losing a seat in the Bundestag overall.[21] The anticipated tactical voting in Dresden I does indeed seem to have occurred as Andreas Lämmel (CDU) won the constituency with roughly 37% of the de:Erststimme (~ constituency vote) while his party won only 24.4% of the de:Zweitstimmen (~ list vote) in the constituency, with the center-right FDP receiving 16.6% - more than one and a half times their federal vote share of 9.8%[22]

This led to another ruling by the German Constitutional Court in 2008 which ruled that the existing federal electoral law was unconstitutional in part as it violated the principle of one person one vote and produced an overly opaque relationship between the numbers of votes cast and seats in parliament.[23][24][25][26] However, the Court also allowed for a three year deadline to change the electoral law, allowing for the 2009 German federal election to be held under the previous set of rules.

The electoral reform passed with the votes of the governing "black-yellow" coalition in late 2011 (a few weeks after the deadline set in 2008) - and without consulting the opposition parties - was again ruled unconstitutional by the Constitutional Court.[27][24] Furthermore, the Court clarified that the federal electoral system was supposed to be primarily one of proportional representation and a number of non-compensated overhang mandates above 15 would "dilute" this proportional character.[28][29]

As the Bundestag thus lacked a constitutional electoral mechanism[30] and the 2013 German federal election was coming up, the government agreed to negotiations with the opposition parties, leading to a new electoral law being passed in early 2013 with broad support from all parties in the Bundestag except Die Linke who voted against the reform due to concerns regarding a possible massive increase in the size of the Bundestag due to overhang and leveling seats[31]

On the state level an unclear wording in the state electoral law of Schleswig-Holstein led to different possible assignments of leveling seats to equalize the overhang seats ultimately resulting in the 2009 Schleswig-Holstein state election giving a majority of seats to the Peter Harry Carstensen led "black-yellow" coalition, despite them having won a lower share of the vote than the SPD, Greens, Left, SSW opposition. Following a suit before the State Constitutional Court brought by opposition parties,[32] it was ruled that the electoral law in its then current interpretation did indeed violate the state constitution but that the Landtag was to keep its composition until a new electoral law could be passed (which happened in 2011) after which new elections would be scheduled with enough time for campaigns setting the next election for 2012, two years earlier than if the Landtag had served its full five year term.[33]

Debates about yet another electoral reform soon resurfaced as the Bundestag did indeed grow in size due to the 2013 electoral reform - it had had 622 members after the 2009 election, 631 after the 2013 but swelled to 709 members after the 2017 election. As a result of the 2021 election producing yet more additional members of the Bundestag, 735 seats will have to be fit into the Reichstag building to accommodate all members of the 20th Bundestag. Measures to reduce the size of the Bundestag (caused, in no small part, by overhang mandates and the measures taken to equalize them) were debated during the 19th Bundestag.[34][35]

Look up Overhang in Wiktionary, the free dictionary.

• Underhang seat

• "Overhang seats". Wahlrecht.de. 26 July 2003.