In time for the upcoming general election, Electoral Calculus has upgraded its prediction model. The new model builds on the success of the previous models, but has a number of new features:
The previous model was the Strong Transition Model. It took essentially a uniform national picture and applied to each seat, but with two extra sophisticated features. For declining parties it behaves multiplicatively - in other words, if a party loses a quarter of its support nationally, then it loses a quarter of support in each seat. But gaining parties gain additively taking a set share of votes "released" by the declining parties. Secondly, it divided voters into "weak" and "strong" supporters - and the weak supporters drift away before any strong ones do.
This model works quite well, but the upcoming election has shown up two weaknesses. The first of these problems is caused by the rise of the two new minor parties: UKIP and the Greens. These parties polled only around 1%-3% in the 2010, but are now polling around 6%-16%. This has been mostly at the expense of the Liberal Democrats, who have declined from 24% to 8%. The Strong Transition Model moves Lib Dems votes towards UKIP and the Greens. But this gives, say, UKIP fairly equal strength across the whole country. And it makes UKIP particularly strong in areas of previous Lib Dem strength, such as Scotland and Wales. But this is not accurate, because these are not really areas of UKIP strength, such as Essex and Lincolnshire.
The new model performs a very granular geographic treatment, giving a better prediction of UKIP in each seat. This means there is also more variation in UKIP votes between seats, with the 25%-percentile of vote strength decreasing from 14% to 12%, and the 75%-percentile increasing from 18% to 20%. This means that the semi-inter quartile range (gap between the 75% strongest vote share and the 25% strongest vote share) has approximately doubled.
The top ten UKIP seats for the old and new models are shown below:
|Seat (old model)||Region||Pred UKIP|
|Boston and Skegness||Humberside||23%|
|Wentworth and Dearne||Humberside||22%|
|Cambridgeshire North West||East Anglia||22%|
|Seat (new model)||Region||Pred UKIP|
|Rochester and Strood||South East||30%|
|Boston and Skegness||Humberside||28%|
|Wentworth and Dearne||Humberside||26%|
|South Holland and The Deepings||Humberside||26%|
|Cambridgeshire North East||East Anglia||26%|
|Louth and Horncastle||Humberside||26%|
We see that the greater range of the new model means that the top 10 seats have more predicted support than the equivalent top 10 seats under the old model. This can also be seen in the following table of average UKIP predicted votes over the various regions, under both the old and new models.
Humberside, Essex and the south of England are more UKIP than an even geographic assumption implies. On the other hand, London is much less UKIP supporting, apart from London boroughs close to Essex.
Let's look at the Greens to see what geographic variation their support has. Similarly the UKIP, the semi-inter quartile range approximately doubles in width from 1.7% (old range from 5.1% to 6.8%) to 3.1% (new range from 4.1% to 7.2%). This shows that the new model allows for more geographic variation than the straight STM.
The top ten Green seats for the old and new models are shown below:
|Seat (old model)||Region||Pred Green|
|Brighton Pavilion||South East||35%|
|Norwich South||East Anglia||20%|
|Lewisham Deptford||South London||12%|
|Lancaster and Fleetwood||Lancashire||10%|
|Hackney North and Stoke Newington||North London||10%|
|Brighton Kemptown||South East||10%|
|Seat (new model)||Region||Pred Green|
|Brighton Pavilion||South East||38%|
|Norwich South||East Anglia||24%|
|Hackney North and Stoke Newington||North London||16%|
|Lewisham Deptford||South London||16%|
|Hackney South and Shoreditch||North London||15%|
The strongest Green seats are now more strong than previous estimates, with Green support generally about 5% higher. The strong seats are more concentrated in the south of England than before. We can see the regional breakdown in the table below.
Strong regions for the Greens are in the West/South West, London and the South East. Weaker regions for the Greens are Scotland, Wales and the north of England.