TWO polls, two seemingly very different implications. A YouGov poll suggesting that Labour and the SNP would be neck-and-neck in a General Election and an Ipsos poll implying a substantial SNP advantage in Westminster seats.
How do we reconcile these two results, and what can we meaningfully take away from them?
Firstly, the two polls differ in important ways. The Ipsos poll is a standard political poll that suggests that 41% of Scottish voters would vote SNP if a General Election were held tomorrow, with 29% voting Labour, 17% voting Conservative, 6% voting LibDem, and 3% voting Green.
You can take those figures and use various methods to predict how many seats each party would win. Using a few different “strong transition models”, we get a prediction that the SNP would lose a handful of seats, down to around 40, while Labour would pick up enough seats to end up with around 15.
The YouGov poll uses a very different method. Through their online panel, they recruited a representative sample and then use a technique called multi-level regression and post-stratification (also known as MRP) to estimate the vote shares that each party would achieve on a constituency basis, rather than nationally.
To reach that estimate they use what they know from their poll about how different demographics would vote, combined with what we know about the demographics of the electorate in different constituencies.
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That method suggests that the SNP would win 27 seats, losing 23 to Labour – who would finish on 24 seats. A much, much tighter election than can be projected from the Ipsos poll, and one in which the SNP would experience much greater losses.
Those numbers are not dramatically different from what we would expect from YouGov’s most recent “traditional” poll in April. Using the same method used to project the Ipsos poll results, we would expect the SNP to win around 29 seats and Labour to win around 22.
But that YouGov poll was not that much different from Ipsos’s poll. The SNP were predicted to win 37% of the vote nationally, four points lower than in Ipsos’s poll, and Labour to win 28%, one point lower than Ipsos’s finding.
The British Polling Council notes that the practical margin of error in polling has historically been around 4%, meaning that those differences could largely be down to random error.
So, why such dramatic differences in seat projections?
The answer is that many of the seats that Labour is projected to gain from the SNP in YouGov’s MRP poll are extremely tight affairs. Of their 23 projected gains, 12 – more than half – would be won by less than five points.
In fact, just one of those seats – Coatbridge, Chryston and Bellshill – would be won by more than a 10-point margin.
And Rutherglen and Hamilton West – widely expected to be won by Labour should a recall petition against Margaret Ferrier succeed in triggering a by-election – is modelled to be won by Labour by just six points.
So, what does all this mean? As the polls have narrowed, around two dozen currently SNP or Alba-held seats have come within reach for Labour – but they have not gained enough ground, yet, to make those gains safe.
If the current polls hold until the next election, the SNP and Labour will find themselves engaged in two dozen closely fought contests in battleground constituencies across Scotland.
A slightly better national environment for Labour would see them making significant gains and closing the gap with the SNP to just a few seats.
A slightly better national environment for the SNP would limit their losses to a handful of seats, while also picking up a couple from the Conservatives.
Because of this, small differences in polling will produce big differences in seat predictions.
They will look contradictory but will simply reflect how close the next General Election could be in Scotland.
Labour could make sweeping gains – it could even become Scotland’s largest party at Westminster. It could also fall short of such a performance, with the SNP’s dominance of Scotland’s Westminster representation continuing.
The difference would be just thousands of votes in the right places – the definition of razor-thin margins.
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