How AMS/MMP Actually Works

by Elias Blum

The various elections taking place across the UK today (5 May 2016) use a total of five different electoral systems:

  • AMS/MMP for Scottish Parliament, Welsh Assembly and London Assembly
  • STV for the Northern Ireland Assembly
  • Supplementary Vote for Mayors and Police Commissioners.
  • A mixture of FPTP and Bloc Vote for English local councils

This would be confusing enough, even without the fact that precious few people in Scotland seem to understand how the electoral system used for the Scottish Parliament actually works. So I thought I would have a go at explaining.

In the time-honoured tradition, I will use a simplified ‘Ruritanian’ analogy.

In the imaginary land of Ruritania, parliament has 100 seats.

  • 50 are awarded on the basis of first-past-the-post in constituencies.
  • 50 are awarded on the basis of a national list by proportional representation.
  •  There are four parties: Red, Green, Yellow and Blue.
  • Each voter has two votes: one for the constituency and one for the list.

Now let’s imagine that the results of the 50 constituencies are as follows:

  • Red wins 5 constituencies.
  • Green wins 2 constituencies.
  • Yellow wins 35 constituencies.
  • Blue wins 8 constituencies.

And let’s assume that the results of the lists are as follows:

  • Red wins 20%
  • Green wins 10%
  • Yellow wins 45%
  • Blue wins 25%

Now – this is the important bit and the bit many people don’t seem to understand – the overall distribution of seats is principally determined by the LIST VOTE on the basis of proportionality. So, with a 100-member parliament, the parties are entitled to the following number of seats:

  • Red: 20
  • Green: 10
  • Yellow: 45
  • Blue: 25

Now, that means that each party is entitled to a number of list seats so that its TOTAL NUMBER of seats is equal to its entitlement set out above, so:-

  • The Red party is entitled to 15 list seats (to add to the 5 constituencies it has won, bringing its total to 20).
  • The Green party is entitled to 8 list seats (to add to the 2 constituencies it has won, bringing its total to 10).
  • The Yellow party is entitled to 10 list seats (to add to the 35 constituencies it has won, bringing its total to 45).
  • The Blue party is entitled to 17 list seats (to add to the 8 constituencies it has won, bringing its total to 25).

So, for 45% of the votes, the yellow party won only 10 list seats. But for 20% of the votes, the red party won 15 list seats. On that level, it looks unfair. But – and again, this is the important part – the lists are compensatory: so the overall result, once you add the list and constituency seats together, is fair.

The Scottish system differs from this in detail – there are regional lists, not one national list, for example, and there are more constituency seats than list seats – but the principle is the same. It results in a broadly proportional outcome, where each party gets a TOTAL number of seats to equal its share of the list vote.

 

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