When pollsters get together and talk about the EU referendum, it doesn’t take long before the conversation gets onto turnout.
The debate’s well explored – 1 in 4 sentences in this BuzzFeed article mentioned turnout – and has mostly concluded that the issue helps Leave. But I think the debate has underestimated something that helps Remain.
YouGov’s Freddie Sayers sets out well here the argument that turnout hurts Leave. As he says, Leave supporters are demographically more like people who vote, while Remain supporters – on average, younger people – look more like people who stay at home.
Polls already take this into account as far as possible. If someone says they’re not certain to vote, pollsters either discount them entirely or weight down their response.
The trouble is, polls before an election usually find that more people say they’re certain to vote than actually turn out. The ones who don’t live up to their word tend to be younger.
So, if this is replicated in the EU referendum, Remain may find that many of their younger supporters don’t actually vote, despite saying they would definitely do so, and so Remain might underperform their polls. Given that online (but not phone) polls currently find the race to be neck-and-neck, that could be crucial.
I don’t dispute this. But there’s another aspect that could be at least as important.
Turnout in Scotland was 85%, so slightly more than 10% of those who said they would definitely vote in fact didn’t do so. But more people voted on 18 September 2014 than, two months before, had said they were certain to do so.
If something similar happens with the EU referendum polls, in mid-June we would see something like 75-82% saying they’re going to vote (and turnout would be around 70%).
One reason that could change the balance of the race is that stated turnout of Remain supporters has more scope to increase from where it is now than turnout of Leave supporters does. In ICM and Mori’s latest polls, 67-70% of Remain backers said they were certain to vote, while 74-80% of Leave supporters said the same.
So there are more people who support Remain but don’t currently think they’ll vote than there are who support Leave and don’t plan to vote. If turnout expectation increases, Remain’s support has more room to grow, without having to win over any undecideds or Leave supporters.
What I think this means in real terms is that Leave supporters tend to be more enthusiastic and already say they’re going to vote. Remain supporters are more grudging and haven’t yet decided to vote – but over the next two months a growing proportion of them might think it’s worth the effort.
When people start paying attention
But perhaps the Scottish referendum was so different from this one that we can’t learn much. Is it really likely that turnout expectation will increase for the EU referendum like it did in Scotland? There’s no way to be sure, but I think it’s a reasonable assumption (though I’m not claiming turnout will be quite as high).