There was an important way in which the opinion polls got it wrong in the EU referendum. The areas that were strongly pro-leave voted even more decisively to leave than expected. The areas that were strongly pro-remain also voted more decisively.
So Scotland and London voted overwhelmingly for remain. Industrial, and former industrial, areas in England and Wales voted overwhelmingly in favour of leave.
So why this extreme form of polarisation?
Psychologists have long known about a phenomenon called group polarisation.
Groups behave differently from individuals. You can call it groupthink or crowd compliance, but we know that groups can form a view that is more extreme than the view held by most of its members.
Group polarisation is where a group exaggerates the average view held by the group's members. For example, a number of people who are mildly risk averse, can form a group that is paralysed by indecisiveness.
A number of people who are inclined to take a mild risk from time to time, can collectively create a group that takes reckless risks. See: Risky Shift Phenomenon
In the age of the Internet, groups form like never before. Ironically, considering the internet is fundamentally about global communications, local groups on Facebook are highly popular.
Is it possible that this had the effect of exaggerating the most common view held previously, whooping up strength of feeling, sucking up the undecided in its wake?
By Michael Baxter, economics blogger