MSPs are chosen for the Scottish Parliament using an electoral system called the Additional Member System or AMS. AMS is a form of proportional representation which aims to give political parties a share of representatives (MSPs in Scotland) in proportion to their share of the vote.
The way in which AMS works
With AMS voters are given a ballot paper which asks them to record two (‘X’) votes.
The first vote is for an area or constituency MSP. In the constituency vote, the person with the most votes wins. There are 73 constituency MSPs.
Under AMS voters are also given the opportunity (a second vote) to vote for a political party. Once all the first votes are counted and constituency MSPs elected, this second vote is used to make the overall representation of each of the political parties fair.
How does the second vote work?
After all the constituency votes are counted, additional MSPs are allocated to each of eight Scottish parliamentary regions to make the overall result fairer to all parties.
For example, in 2016 the Conservative Party were given two additional (or list) MSPs in the North East Scotland region as they failed to return any constituency MSPs. This gives Conservative Party voters fairer representation in proportion to their political support in the North East of Scotland.
There are 56 additional regional MSPs (7 per region). When added to the 73 constituency MSPs this makes 129 MSPs altogether.
Advantages of AMS
More choice: Voters have more choice when they go to vote. In the first vote they may choose a local representative from one party but in their second (list) vote they may switch to a different party.
Fairer to all parties / proportional: The overall result is fairer to all parties or more proportional. For example, the 2016 Scottish Parliament elections saw a maximum difference of 5% between the voted received and the MSPs returned.
More views represented: It is possible that a greater number of parties will be represented in the government as a coalition is more likely.
Every vote counts: Although voters may find their chosen constituency candidate has little chance of winning, their second vote will help to elect a representative from the party of their choice.
Disadvantages of AMS
Complex: Elections are more complicated with two votes and in deciding which candidates are elected from the regional list.
Multiple representatives: Having several MSPs to represent each voter is confusing for some voters.
Coalitions more likely: Coalition or a minority government (SNP 2006-2011), with compromise politics, is more likely as it is difficult, although not impossible, for one party to form a majority government.
Not most proportional system: Although AMS is a proportional representation (PR) system, it is not the most proportional of systems. For example, the SNP received around 44% of the vote in the 2016 Scottish Parliament election but returned 49% of MSPs (63 out of 129) while the Liberal Democrats received around 7% of the vote but only returned 5 MSPs (4%).
Parties control regional lists: Second vote is used to select representatives from a list to make the overall result proportional. However, it is the political parties which decide the order of the candidates on the list.