Additional Member System (AMS)
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Last updated 22 Mar 2021
The Additional Member System (AMS), also known as Multi-Member Proportional (MMP)is a hybrid election system, combining FPTP and the Party List, used in the Scottish Parliament, Welsh assembly and the Greater London Authority.
From 2003 to 2005 it was used for local elections in Scotland. The Jenkins Commission partially recommended it for UK General Elections (see later). Germany uses MMP for the Bundestag elections.New Zealand adopted it in 1993, in preference to its FPTP system.
In Additional Member Systems, the voter gets two votes - One vote is cast for a constituency MP, under FPTP rules. Some seats (half, in the German system, 3/4 in the Italian, 14/25 in the GLA) are filled this way. The other vote is cast for a party. The rest of the seats are filled this way, on a strictly proportional basis, using a national list, a number of regional lists, or even STV.
AMS does have the effect of creating 2 classes of MP: only one with a constituency to look after. The PR MP has no personal mandate. The larger the proportion of PR seats, the greater the proportionality but the less of a link with an individual MP. Voters can also “split their ticket” (i.e. vote for different parties in the same election). They did this in the Scottish Parliament elections in 1999, the Green party getting several PR seats despite not standing in any constituency seats.
The allocation of PR seats can be influenced by or independent of the result in the constituencies. The two halves of the Bundestag are "watertight".By contrast, in the Scottish Parliament elections, the results in the 73 FPTP seats affect the 56 PR seats. Thus, because Labour does disproportionally well in the former, it gets fewer seats in the latter, by way of compensation. The opposite is so with the Conservatives. The ‘top-up’ system’s aim is either for the party's total number of representatives, including constituency representatives, to be proportional to its percentage of the party vote, or for the allocation of additional party seats to offset all or most of the disproportionate result in the constituencies. This can be shown in the tables below.