From Academic Kids
How overhang seats arise
Under MMP, a party is entitled to a number of seats based on its share of the total vote. If a party is entitled to ten seats, but wins only seven constituencies, it will be awarded three extra seats, bringing it up to its required number. This only works, however, if the party's seat entitlement is greater than (or equal to) the number of constituencies it won. If, for example, a party is entitled to five seats, but wins six constituencies, the sixth seat is called an overhang seat.
Two mechanisms to earn many overhang seats
The two mechanisms to increase the number of overhang seats are
- win a lot of constituencies
- decrease the number of party votes
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, two circumstances in which overhang seats may arise relatively easily:
- 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 religions minorities may also come under this category, particularly if seats are reserved for these groups.
- 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.
Dealing with overhang seats
Overhang seats are dealt with in different ways by different systems. The four main methods are:
- Take the number of overhang seats off from the other parties' seats — A party is simply allowed to keep any overhang seats it wins, and the number of seats awarded to other parties is decreased to compensate. This means that a party with overhang seats has more seats than its entitlement, and other parties have fewer. This system is used in the Scottish Parliament.
- Allow the overhang — A party is allowed to keep any overhang seats it wins, but other parties are still awarded the same number of seats that they are entitled to. This means that a party with overhang seats has more seats than its entitlement, while other parties are no different. It requires that the total number of seats increase, as the overhang seats are effectively "extra". This system is used in the German Bundestag and the New Zealand Parliament.
- Additional balance seats — A party is allowed to keep any overhang seats it wins, but other parties are given additional seats in order that they are not disadvantaged. This preserves the same ratio between parties as was established in the election. It also increases the size of the legislature, more so than for the second option — not only are there are overhang seats, but there are other seats to counteract them. The number of balance seats can be limited, to avoid a too big increase of the house.
- Non-awarding of overhang seats — A party is not allowed to keep any overhang seats it wins, with its number of seats actually being reduced until it fits the party's entitlement. This raises a number of complications, such as the question of which constituency seats the party is not allowed to keep.