Methodology

The predictor on this blog uses Uniform National Swing (UNS) and an option to use Uniform Regional Swing (URS).

UNS is the simplest model of applying opinion poll results to the results of the last election and estimating what impact movements in public opinion have if an election was held tomorrow.  URS follows the same principle as UNS but works at Assembly Regional level - ie the South West, the North etc

Put simply:

1. UNS says that if a party is up 3% nationally, that it will be up 3% in each seat.
2. URS says that if a party is up 3% in a specific region, then it will be up 3% in each seat in that region.

As the National Assembly uses a regional top up system we have been able to offer two methods of entering data:

1. the percentage of the national constituency vote and the percentage of the national regional vote.
2. the percentage of the constituency vote insode a specific region and the percentage of the regional vote insode a specific region.

These options allow for much more accuracy in terms of regional support for specific parties and also allow for some interesting predictions using the regional breakdowns behind the ITV / You Gov monthly opinion poll (NOTE regional opinion polls have a higher error of margin than the national one).

If you do not enter figures for all regions the default will be taken from the national regional prediction - buit where you do enter data this will over ride the national figure.
A similar predictor to the one found here can be seen at Electoral Calculas UK which has a good record of predicting UK elections - although fails to take account of changes in support of Plaid Cymru and so is of limited use for Welsh politics.