by Stephen Fisher and Alan Renwick.
Remain have continued their gentle slide in the polls. Last week our polling average saw Remain drop from 53% to 52%. Now they are on 51% after setting aside Don’t Knows.
The further one-point drop in our polling average has produced a one-point drop in the forecast share of the vote for Remain, from 54% to 53%.
The 95% prediction interval is still ±12 points. We are now forecasting that Remain will win between 40% and 65% of the vote.
The probability that Remain will win the referendum is now down to 68%.
The method behind this forecast is based on the historical experience of referendum polls and referendum outcomes in the UK and on the EU elsewhere, as discussed here.
Our polling average is constructed by taking the most recent poll from each company within the last two weeks. If a company uses both phone and online modes then both the most recent phone poll and most recent online poll are used. This applies just to ICM this week. The current average is based on the results of eight polls from seven companies, of which three were conducted by phone and five online. All polls are adjusted to account for the tendency for phone polls to be more favourable to Remain. This is done by adding 2.2 to the Remain share for online polls and subtracting the same amount for phone polls.