Twitter, I do normally try and behave on here, but sometimes there are very silly claims made about how the Scottish Parliament electoral system works, and debunking those is a democratic good.

Today's Lesson: No, the Pro-Union Parties Aren't Overly Benefiting from AMS

A claim that has been popping up more and more in BBS' mentions is that as there are three Pro-Union parties at Holyrood, they naturally benefit from how AMS is set up, since there are three different parties to spread list seats to.

This is mathematically incorrect.

We can generalise Holyrood elections to state that around about 6% of the vote is enough to secure a regional seat. (Emphasis on generalise - depends on overhang and overall split)

A party winning 30% of the vote will therefore win 5 seats in that region, generally speaking.

If the same 30% is split between three parties, they may not collectively win 5 seats - it'd have to be split between them in neat multiples of 6%.

So, 12%, 12%, 6% would be 2, 2, 1 for a total of 5 seats, nae bother.

BUT

15%, 10%, 5%, would be 2, 1, 0, for a total of 3!

That's some really simple arithmetic you can throw any assortment of numbers into to demonstrate the basic principle, that when delivering proportionality over a relatively small number of seats, more fractured electorates "waste" more votes.

But we have 2016's figures to hand!

If we put the Conservatives, Labour and Lib Dems into one Bloc (in reality, you can't expect all of their voters would fall in behind such a bloc), we get (vs 2016):

Bloc - 67 (+7)
SNP - 57 (-6)
Green - 5 (-1)

Further confirming the original claim is false

Some accusations go further than just the incorrect claim that AMS benefits the Pro-Union parties for being separate, to their separation being a deliberate ploy.

That's obviously silly as each of those parties represents a distinct political tradition going back over a century.

None of this is guidance on how to vote on a partisan basis at Holyrood elections - everyone should do so according to their own conscience.

It's just important to dispel myths when they pop up, as misrepresenting how AMS works may negatively impact the electorate.

In a conclusion that will surprise no one, if you think having an overall seat share at the mercy of how votes split locally is an annoying mathematical quirk of AMS, get you a voting system that delivers national rather than regional proportionality! http://ballotbox.scot/ballot-box-briefing-2-scandinavian-style-proportional-representation