Pollsters consistently under-estimate the ‘status quo’ vote in their final referendum polls

The set of final polls from each pollster published in three recent UK referendum campaigns (Welsh devolution 2011, electoral reform 2011 and Scottish independence 2014) consistently under-estimated the actual vote for the ‘status quo’ option.

Taking the data from the excellent Elections in Wales site, we get:

1. Welsh devolution referendum 2011: poll average 31% no, actual 37% no.
2. Electoral reform (AV) 2011: poll average 64% no, actual 68% no.
3. Scottish independence 2014: 53% no, actual 55% no.

So far, this pattern has not embarrassed pollsters are they’ve got the winner right and in some cases the final fieldwork from a pollster was a good few days before polling day.

But the overall pattern is consistent, and fits with wider international experience – the public usually moves towards the status quo option as polling day nears.