Holyrood List Vote Splitter

If you move the slider in both directions, you will see that both sides of the debate have at least some merit. If the split had been the same as in 2011 (4.4% / 44.0%) then the SNP would have held onto a parliamentary majority (though reduced from 9 to 1). On the other hand if even more SNP votes had shifted to Green then there would have been a larger majority of pro-independence MSPs.

Really the question comes down to what your priority is. If your priority is to secure a majority SNP government at all costs, then you will say that the SNP need to take almost every single pro-indy list vote to ensure that happens. If your priority is to elect more pro-indy MSPs and fewer unionists, then you will say that a vote for the Greens is the way to achieve this.

One weakness in the SNP argument is that they really do need to take a huge portion of the pro-independence list votes in order to get a majority using list seats. To win list seats in most regions the SNP need to win almost all of the pro-indy list votes, while the Greens can make significant gains with just a fraction of those votes. Recent opinion polls suggest it is quite likely the SNP will win zero list seats nationwide, meaning all votes for them will have been for no gain. They also suggest that the SNP have a good chance of securing a majority with constituency seats alone.

Scotland is divided into eight electoral regions, with each region electing seven regional (or "list") MSPs under an Additional Member System.

The segmented bar charts above give an idea of how the seats are allocated. There is a threshold each party needs to reach to get a seat. If you divide a party's vote tally by the threshold, you get the minimum number of seats they are guaranteed. If they don't reach that number with their constituency seats, they are awarded list seats to top them up.

This is a useful way to understand how the Additional Member System works in effect, but it is a simplification and not quite how the seats are allocated in practice. The "threshold" is just an arbitrary number that depends on how the votes (and constituency seats) are distributed.

In practice the seven list seats are allocated in sequence. Each seat is awarded to the party with the most votes on the regional ballot, after applying the following simple formula: total_votes / (n + 1), where n is the number of seats the party has already won in the region, including constituency seats.

This means that if a party has not yet won any seats in the region, n = 0 and their vote tally is divided by one (i.e. it is unchanged). If a party has already won one seat, n = 1 and their votes are divided by two as they go for their second seat. And so on.

This formula makes it much harder to win list seats for a party which has done well on the constituency ballot, as they can in some cases be starting off with their votes being divided by as much as eleven.

To see how the Additional Member seats are allocated in sequence and how this relates to the bar chart, select a region below:

• Highlands and Islands
• North East Scotland
• Mid Scotland and Fife
• West Scotland
• Glasgow
• Central Scotland
• Lothian
• South Scotland

One of the arguments for #BothVotesSNP is that the SNP might not perform as well as expected in the constituency ballot. If this happens, their list votes will act as an insurance policy and they can pick up list seats to replace the lost constituency seats.

Recent polling suggests that this is highly unlikely to happen, and in fact suggests the SNP might even pick up so many constituencies in the South Scotland region that they will lose all three of their list seats there, leaving them with just one list seat in the whole country.

Polls are not a guarantee of support at the ballot box though, so they do not invalidate the argument. It is true that list votes for the SNP can act as an insurance policy in the event that they lose constituency seats. However, if that doesn't happen then those list votes for the SNP will indeed end up gaining no seats in most regions.

By contrast, the Greens are likely to be competitive in the list vote in every region, meaning a Green vote will have value in every region regardless of the outcome of the constituency ballot.

If it's so hard to gain list seats when doing well in the constituency ballot, then how did the SNP manage to get a majority in 2011? They won only 53 constituencies in 2011 but gained a majority due to 16 list seats. So how did they lose that majority in 2016 when they increased their constituency tally to 59?

Some people argue that the SNP lost their majority in 2016 because their list vote dropped from 44.0% to 41.7%, but that does not adequately explain the deficit. If you adjust the slider to give the SNP 44.0% of the list vote in 2016, they regain their majority, but only just. They still drop from 69 seats to 65, and this adjustment to give the SNP two seats costs the Greens four, costing the independence movement two seats overall.

In fact, the two pro-independence parties picked up roughly the same combined list vote share in 2016 as in 2011 (losing 0.1% overall), but lost two seats. This is not because of votes going from SNP to Green. While the SNP lost 2.3% and the Greens gained 2.2%, if you try adjusting the slider you will see that there is no way to make the two parties' tallies add up to more than 69 - unless, that is, you move even more votes from SNP to Green.

In fact, the majority for the SNP in 2011 was down to nothing more than a fluke of arithmetic. In Holyrood's quasi-proportional voting system it really shouldn't be possible to get a result like 2011, where a single party picks up 53.5% of the seats with 44.0% of the list vote, unless they pull off a nearly clean sweep of constituencies.

The reason why it happened in 2011 is because other parties "wasted" a lot of votes. Some of these votes were "wasted" by smaller parties who did not pick up enough votes to get any seats, but most were due to the three establishment unionist parties picking up nearly enough votes to get one more seat and falling just short. This happened to Labour and/or the Tories in every region where the SNP won a majority of seats, but the most extreme case was North East Scotland.

In North East Scotland, the SNP won every single one of the ten constituency seats. Winning another one on the list shouldn't have been possible, but they somehow pulled it off. The Additional Member System is supposed to produce a reasonably proportional result in each region, but the SNP won 64.7% of the seats with 52.7% of the vote, just because of the way the votes for the other parties were distributed.

Between them, the three unionist parties had enough votes to pick up 1.8 more seats, but none of them got enough to reach the threshold and take the last seat. There is no way to predict this or to exploit or mitigate it through tactical voting, it's just luck.

The numbers on this page are based off of the results from the 2016 election. As they did not exist at that point in time, the Alba Party do not feature. This page is only intended to illustrate some of the arguments around tactical list voting in principle, with the SNP/Green vote breakdown for 2016 as an example.

If Alba can build up to have a similar level of support to what the Greens had in 2016 (i.e. around 6%) then they can be competitive in every region and the arguments laid out here for voting Green would also apply to them. Polling so far suggests that they are not at this level yet. If they end up taking around 3% then there is a risk is that they could take a lot of votes from other pro-independence parties but fail to achieve any seats with those votes.

If every SNP supporter was to vote Green and thereby secure a huge independence "supermajority", picking up around 75% of the seats with only around 50% of the vote, one obvious objection is that this would be "gaming the system". If we are trying to achieve independence for Scotland, we should be promoting the strengths of Scotland's institutions, not trying to exploit their weaknesses.

On the other hand, the SNP gained 95% of all seats in Scotland with just 50% of the vote in the 2015 Westminster election. If Holyrood's halfway house attempt at a proportional voting system is flawed, it is still better than Westminster's winner-takes-all system. And under that system, Green supporters in Scotland are very used to lending their votes to the SNP in constituencies where the choice is between the SNP and a unionist candidate.

However a more important point to note is that voters aren't pawns on a chess board. While it's interesting to move votes around and see how the results would change, nobody gets to do that in real life. Each voter will make up their own mind who they want to vote for. And while many independence supporters are sympathetic to both the SNP and the Greens and can flit between them based on tactical concerns, others strongly disagree with every party other than their first choice and have no intention of "lending" their vote to anybody.

This leads us nicely into another argument: there is no such thing as a "wasted vote". In the purest, most idealistic perspective, voting is an expression of our hope for the kind of future we want to live in. As long as we cast it for a party which truly encapsulates that hope, it is never wasted. Others take a more pragmatic view; that no political party will ever perfectly reflect all of your principles, voting is a means to an end, and you should cast your vote in whichever way has the best chance of making a positive impact.

At the end of the day it's up to you. Your vote belongs to you and nobody else. Nobody gets to tell you what to do with it.