Constituency Forecasts is our model for projecting the 2017 UK general election result. Unlike forecasts based on uniform, or adjusted uniform swings, we use a mathematical tool called Regional Variants, or RegVar (after the brass band). RegVar attempts to aggregate together data from previous elections to predict how a particular seat will behave relative to the UK as a whole, and to nearby seats. In theory, this means that if Southwark sneezes, then Kate Hoey catches a cold.
The aim is to avoid the kinds of systematic polling errors that can be caused by small errors in the national polls. As Ed Miliband will tell you, more votes doesn’t always mean more seats under first past the post. Similarly, we saw Hillary Clinton rack up a two million popular vote lead while losing the Electoral College – she would have needed her voters to be less than 2 per cent more efficiently distributed to win the day, and the presidency.
RegVar works first by taking the national vote share and comparing it with the regional vote share, simulating the unequal distribution of votes. In the South East, you would expect the Tories to pick up twelve votes for every ten they received nationally, while they might get only seven in the North West. Consequently, for every 100 Tory votes nationally, we expect perhaps 120 Tory votes in Guildford.