AMS - the Quick Explanation

Unlike elections to the UK Parliament, the Scottish Parliament is elected by a system of proportional representation (PR), as is the norm in democracies across the world. Our particular version is known as the “Additional Member System” (AMS).

That’s means it’s a mixture between two different kinds of election, with two votes – the Constituency Vote and the Regional List Vote. Together, these elect a total of 129 Members of the Scottish Parliament (MSPs).

The Constituency Vote

  • Scotland is divided into 73 Constituencies.
  • Each Constituency elects one MSP.
  • The candidate with the most votes wins.

You might also hear this referred to as the “First Vote”, and it uses the familiar FPTP system to elect an MSP. It doesn’t matter whether the candidate wins by 1 vote or 10,000, whether they get 29% or 60% of the total vote, all that matters is they came first.

Although this is simple, it’s also a very unfair system. It means most voters aren’t represented. That’s partly why when the Scottish Parliament was being set up, it was decided not to use this system alone. 

The Regional List Vote

  • Constituencies are grouped into 8 regions, of 8 to 10 constituencies.
  • Each region elects 7 MSPs.
  • These seats are allocated proportionally, taking into account how many Constituency seats each party won in that Region.

This one might also be referred to as the “Second Vote”, and it ensures that the diversity of voters is more accurately represented than is possible under FPTP. Although the two votes are separate, the seats they elect aren’t. The list seats are allocated so as to deliver an overall balance across the whole region, including constituency seats won.

To do this we use something called the “D’Hondt method”. I promise this isn’t anywhere near as complicated as the fancy name suggests. You just divide each party’s regional vote by one more than the number of seats it has won so far in that region, including constituencies.

This basically means that the more constituency seats a party wins, the fewer list seats it will win. Remember, that’s what makes this system fair – if a party has already got lots of constituency seats, their voters are already represented. The list seats then make sure that other voters get their fair representation.

Depending on region and the results for other parties, the rough regional vote share required per seat is about 5-6%. So a party that wins 17% of the regional vote would probably be entitled to three seats in total. If they didn’t win any constituencies, that would be three list seats. If they won one constituency, it’d be two list seats, and so on.

You can also read a bit more about how the system works, and how to communicate it, in this little guidance paper.

So, how should you vote?

I’m occasionally asked to give some voting advice. As a non-partisan project, the only advice I will ever give is this:

Vote for the party (or candidate) you most want to.

Ahead of both the 2016 and 2021 elections, social media was swirling with chat about tactical voting. We know that it came to basically nothing last time – RISE went hardest on it and achieved 0.5% of the vote, 0.1% up on the SSP’s 2011 performance, whilst Green gains match extremely poorly to the SNP’s losses.

Let’s be clear and honest: Scottish politics social media is a bubble. Most voters will go out and do exactly as I have suggested, and vote for who they want to. Tactical voting, where it occurs, is far more likely to be on the constituency side of things, where long established patterns are much easier to predict. 

AMS - the more Detailed Explanation

Let’s take the Lothian region from 2016 as our example to really dive into the numbers. This region saw four different parties win constituencies, so it’s nice and diverse for illustrating how the system works.

Lothian Constituency Votes

There are nine constituencies that make up the Lothian region, and the result of the constituency vote in each was as follows:

The SNP won six constituencies, and Labour, the Conservatives and Liberal Democrats each won one each. If this election was pure First Past the Post, the SNP would have two-thirds of the seats here even though it wasn’t anywhere near winning two-thirds of the votes. That would be fundamentally unfair, and that’s where the regional list comes in.

Lothian Regional Vote

Now we know who has won each of the constituencies, we can allocate the list seats, to make them more reflective of votes cast. To do so, we first need to see how many regional list votes were cast in total.

This is when we start using the D’Hondt method, by dividing each party’s share of the vote by one more than the number of constituency seats they’ve won.

  • The SNP won 6 constituencies, so their vote is divided by 7.
  • The Conservatives won 1 constituency, so their vote is divided by 2.
  • Labour won 1 constituency, so their vote is divided by 2.
  • The Liberal Democrats won 1 constituency, so their vote is divided by 2.
  • No one else won any constituencies, so their votes aren’t divided.

That then gives us this (removing the parties that clearly don’t have enough votes for clarity):

Since the Conservatives have the highest total here, they receive the first regional list seat. We add that to their total, giving them 2 seats overall so far, and therefore for the next round of allocation their share is divided by 3.

This time the Greens have the highest total, so they receive the second regional list seat. That gives them 1 seat overall so far, and therefore for the next round of allocation their share is divided by 2.

Labour have the highest total, so they receive the third regional list seat. That gives them 2 seats overall so far, and therefore for the next round of allocation their share is divided by 3.

The Conservatives have the highest total, so they receive the fourth regional list seat. We add that to their total, giving them 3 seats overall so far, and therefore for the next round of allocation their share is divided by 4.

Labour have the highest total, so they receive the fifth regional list seat. That gives them 3 seats overall so far, and therefore for the next round of allocation their share is divided by 4.

The Conservatives have the highest total, so they receive the sixth regional list seat. We add that to their total, giving them 4 seats overall so far, and therefore for the next round of allocation their share is divided by 5.

The Greens have the highest total, so they receive the seventh and final regional list seat. We add that to their total, giving them 2 seats overall. That means the final share of seats is as follows:


6 SNP (all Constituency)
4 Conservative (3 Regional, 1 Constituency)
3 Labour (2 Regional, 1 Constituency)
2 Green (all Regional)
1 Liberal Democrat (Constituency)

And if we compare the share of votes with the share of seats, we can see it’s pretty close. It’s not 100% accurate, because 16 seats in total isn’t enough for perfect accuracy, but it’s much better than if we had FPTP only!