“Silver Trap” UK Style: Brexit Odds Way Off?

We now have an update from Matt Singh at Number Cruncher Politics on the odds of Brexit.

Despite massive shifts in two polls by The Guardian (online and telephone polls both show Brexit in the lead), and a Telegraph poll yesterday which showed the Brexiteers only trailing by 6 points, down by 15 points the week before, Singh bumped up the odds of Brexit by a mere 2 percentage points to 21%.

Is Singh misreading the polls and a sentiment change just as Nate Silver did with Donald Trump in the US?

Please consider Is Britain heading for Brexit? Latest polls.

Today we got a pair of parallel phone and online polls from ICM for the Guardian. Online showed a 3 point lead for Leave, which is pretty unremarkable. But what was really fascinating was the big swing in the phone poll, compared with a fortnight ago, to show Leave 3 points ahead there too.

Coming on the heels of yesterday’s ORB/Telegraph poll, which showed the Brexiteers only trailing by 6 points (having trailed by 15 points the week before), certainly got people talking. Is this a Leave surge on the back of last week’s migration figures?

It could be. But there are a couple of reasons to be cautious. First of all, while substantial shifts in public opinion can and do happen, polls often overshoot, even when there is an apparent reason. When the draft EU deal was published in February, we some some huge Leave leads that didn’t last. A move has to be genuine and sustained, and very often big event-driven swings (see voting intention polling after party conferences and budgets) often haven’t been.

The other complicating factor is that the fieldwork for these polls was done over a bank holiday.

The effect on the forecast is relatively small – the central projection is now 55-45 and the Brexit probability has increased a couple of points to 21%. This illustrates the whole point of a polling average – to smooth out sudden moves. But if we continue to get polls like today’s, expect the forecast to move down and the Brexit probability to move up quite a bit further.