SM - Supplementary Member

There are 120 Members of Parliament. There are 90 electorates, including the Maori electorates.

Each elects one MP, called an Electorate MP. The other 30 seats are called supplementary seats. MPs are elected to these seats from political party lists and are likely to be called List MPs.

Each voter gets two votes. The first vote is to choose the MP the voter wants to represent the electorate they live in. This is called the electorate vote. The candidate who gets the most votes wins. They do not have to get more than half the votes.

The second vote is for the political party the voter chooses. This is called the party vote. The share of the 30 supplementary seats each party gets reflects its share of the party vote. For example, if a party gets 30% of the party vote, it will get about 9 List MPs in Parliament (being 30% of the 30 supplementary seats) no matter how many electorate seats it wins.

This makes SM different from MMP where a party’s share of all 120 seats mirrors its share of the party vote. Under SM, one or other of the major parties would usually have enough seats to govern alone, but coalitions or agreements between parties may sometimes be needed.

SM in Detail

There would be 120 Members of Parliament.

Types of MPs?

There will be two types of MPs – those elected from electorates and those elected from party lists.
The country will be divided into 90 electorates, each electing one MP. They will be called the Electorate MPs. On the basis of current census data, the 90 electorates would consist of

  • 21 South Island general electorates
  • 60 North Island general electorates
  • 9 Maori electorates

The remaining 30 seats in the 120-member Parliament are called supplementary seats. MPs are elected to these seats from political party lists published in advance and are likely to be called List MPs.

How would you vote?

Each voter has two votes.

The first vote is to choose the Electorate MP the voter wants to represent the electorate they live in. Voters put a tick  next to the name of the candidate for whom they wish to vote.

The second vote is for the political party the voter chooses. This is called the party vote. Voters put a tick  next to the name of the party for which they wish to vote.

How are MPs elected?

In the 90 electorate seats, MPs are elected using the First Past the Post (FPP) voting system. The candidate who gets the most votes wins. They do not have to get more than half the votes. (For more information, see the section on FPP.)

The share of the 30 supplementary seats each party gets is about the same as its share of the party vote.
For example, if a party gets 30% of the party vote, it will get about 9 List MPs in Parliament (being 30% of the 30 supplementary seats) no matter how many or how few electorate seats it wins.

This is different from MMP because under that system a party’s share of all 120 seats is about the same as its share of the party vote. For example, under MMP if a party gets 30% of the party vote it will get about 30% of 120 seats (36). Under SM it would get only 30% of the 30 supplementary seats (that is, 9) -- plus, of course, whatever number of electorate seats it won.

What would Parliament look like?

Under SM, there is an element of proportionality – in the supplementary seats, but normally the overall result is not proportional (that is, it is not the same as the party vote).

Larger parties would likely be over-represented in Parliament and smaller parties under-represented. This is because ¾ of the seats in parliament are elected by FPP, and because the party vote determines a party’s share of the 30 list seats only.

Small parties with a minimum degree of support could qualify for a share of the 30 supplementary seats.

The main features of SM are illustrated in the 2005 and 2009 elections to the House of Representatives of the Japanese Parliament. It has a total of 480 seats – 300 single-member electorate seats (elected by FPP) and 180 supplementary list seats (elected by proportional representation).
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In both 2005 and 2009, the party that won the largest number of votes did not get more than half of either the electorate votes or the party votes, but managed to win more than 60% of the seats in the House of Representatives.

In 2005, the Liberal Democratic Party won 48% of the electorate votes and 38% of the party votes and gained 62% of the seats. Four years later, the Democratic Party of Japan won 47% of the electorate votes and 42% of the party votes, and a total of 64% of the seats in the House.

The Japanese Communist Party provides a good illustration of how small parties can fare under SM. In 2005 it won 7% of both the electorate and the party votes. The Communist Party's electorate votes gained no seats in the House of Representatives, but its party votes meant it won 9 supplementary (or List) seats. Similarly, the New Komeito party won more than 11% of the party votes in 2009, which gave it 21 supplementary seats – 4.4% of all the seats in the lower house of the Japanese Parliament.

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What type of government is usually formed?

Under SM, one or other of the major parties would usually have enough seats to govern alone, but coalitions or agreements between parties may sometimes be needed.

After the 2005 election in Japan, for example, the Liberal Democratic Party had enough seats to govern on its own. Similarly, after the 2009 elections the Democratic Party of Japan also had enough seats in the House of Representatives to form a single-party majority government.

Where is SM used?

SM is used for parliamentary elections in Japan and South Korea, as well as in several new democracies, including Croatia and Georgia.

What are other names for Supplementary Member (SM)?

SM voting systems are usually referred to as Parallel electoral systems and are sometimes known as Mixed Member Majoritarian (MMM) voting systems to distinguish them from Mixed Member Proportional (MMP) systems. Political scientists sometimes classify SM as an example of a semi-proportional representation voting system.

 

 

Last updated: 20 October 2015