Supplementary Member

The Supplementary Member system (SM) is a voting system that combines first past the post (FPP) with proportional representation.

Table of contents

1 Procedure 2 Advantages and Disadvantages 3 Countries where used

Procedure

Under SM, a majority of seats in the legislature are filled by FPP, with single member constituencies. The remainder are filled from party lists, with parties needing to have polled 5 per cent of the vote in order to achieve representation, as under the Additional Member System (AMS).

Unlike AMS, however, where party lists are used to achieve an overall proportional result in the legislature, under SM, proportionality is confined only to the list seats. Therefore, a party that secured 5 per cent of the vote will have only 5 per cent of the list seats, and not 5 per cent of all the seats in the legislature.

Advantages and Disadvantages

SM allows smaller parties to secure representation in the legislature without having disproportionate power, as would be the case under an entirely proportional system. A criticism of proportional voting systems, is that the largest parties need to rely on the support of smaller ones in order to form a government. However, smaller parties are still disadvantaged as the larger parties still predominate.

Countries where used

SM is currently used for elections to the Kukhoe (National Assembly) in South Korea.