The electoral system used for The Scottish Parliament is often described as complex, but in reality, it rests on a simple principle.
One vote rewards party dominance. The other limits it.
The system is known as the Additional Member System. It combines constituency elections with a proportional regional list. I tis sometimes referred to as mixed member proportional representation.
Every voter receives two ballot papers. One is a vote for the constituency MSP, and the other for the party or independent candidate who will then be members of the regional list.
Of the 129 MSPs, 73 are elected in constituencies and 56 are elected from regional lists. There are eight regions in Scotland and seven MSPs will be elected to each regional list.
It is through the constituency vote that the Scottish National Party (SNP) has built its modern political strength in the past.
How does it works
The constituency vote operates on a first past the post basis. The candidate with the most votes wins, regardless of overall share.
This system strongly favours parties with broad support across the country. In 2021, the SNP secured 62 of the 73 constituency seats.
The Conservatives won five, the Liberal Democrats four and Labour two.
Those victories are critical. Constituency seats are decided outright, without adjustment, and they form the foundation of power at Holyrood.
The result is that the SNP has been able to turn a plurality of votes into a dominant position in terms of seats, particularly in the Central Belt.
The regional list
The second vote tells a different story. The regional list exists to correct the imbalance created by constituency results. Seats are allocated using a proportional system which takes account of how many constituencies each party has already won.
Parties which dominate constituencies, such as the SNP, typically win few or no regional seats. Parties that struggle to win constituencies rely on the list to secure representation.
Voters cast their regional vote for parties rather than named individuals (unless a candidate is standing as an independent).
This is the system working as it was intended. Without the regional list, constituency dominance would translate into overwhelming control of Parliament. With the proportional system in place, smaller parties can retain a presence in parliament.
The impact
The political consequence is clear. It is difficult for any single party to secure an outright majority.
That barrier has only been overcome once. In 2011, under the leadership of Alex Salmond, the SNP won a majority government, paving the way for the Scottish independence referendum.
Elections produce a different outcome each time. The largest party dominates constituencies, but falls short of a majority once regional seats are allocated.
Current projections suggest that pattern will continue, with the SNP likely to remain the largest party but (according to the Norstat poll for The Sunday Times) will be reliant on support from other parties, including the Greens and Independent MSPs, to form a government.
How the regional list vote calculation works
Votes on the regional list in elections to The Scottish Parliament are allocated using the D’Hondt method, which is designed to balance the results of the constituency vote.
In a particular region a party’s total regional vote is divided by the number of constituency seats it has already won in that region plus one.
The party with the highest resulting figure is then awarded a regional seat, after which its total is divided again using the updated seat count.
The process for the second round the total number of regional votes for a party is divided by the total number of seats won by that party in the region (constituency and regional) plus one.
This process is repeated until all seven regional seats are allocated, ensuring that parties which have won fewer constituencies receive a greater share of the list seats and that the overall result more closely reflects how people voted.
