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Professor Paul Taggart

Dr Kai Oppermann

Donald Rumsfeld famously talked about ‘known knowns’ and ‘known unknowns’. Looking systematically at referendums and at the experience of these in Europe, we can learn from what has happened in other European referendums to help us in looking at what may happen in the UK’s referendum on EU membership. There may be uncertainty ahead but we can know what we don’t know from previous experience. We suggest that there are six lessons we can learn.

Referendum outcomes are hard to predict

The one ‘known known’ we have is the state of the polls at the outset. But early in the campaign, opinion polls tell us very little about what the outcome of the referendum will be on 23 June. Around 20% of voters are still undecided. More than that, voting behaviour in referendums is much less settled and more fluid than in general elections. This is because

party affiliation and long-term party identification matter less in referendums whereas campaign effects tend to matter more. In particular, the referendum campaign will increase the level of information the average voter holds about Britain in Europe. The campaign only really started after the European negotiations about the British demands were concluded on 19 February, and voters will hear a lot about the EU from both sides of the debate between now and the referendum. Early polls reflect the balance of opinion in a relatively information poor environment, but the vote will take place in a quite information rich environment. This might swing a significant number of voters – in one direction or the other.

Turnout matters

EU referendums have been won or list depending on the ability of the opposing sides to mobilise and to turn out the vote. Good examples are the two Irish ‘No’ votes on the treaties of Nice (2001) and Lisbon (2008). Both votes involved low turnouts – 35% in the case of Nice, 53% on the treaty of Lisbon – which were primarily down to the poor mobilisation of the ‘Yes’ camps. When the two treaties were put to second referendums in 2002 and 2009, the ‘Yes’ campaigns learned the lessons from their previous defeats and were better at mobilising their supporters. In consequence, the turnout increased by 15 points (Nice) and 5 points (Lisbon) which in both cases was sufficient to overturn the results of the first referendum and to deliver ‘Yes’ votes.

The difference between the Irish experience and the current referendum campaign in Britain, however, is that we should not expect a significant gap in the mobilisation of the ‘remain’ and ‘leave’ campaigns. There can be little doubt that the stakes are very high and that the question of British EU membership will dominate the UK political debate. Mobilisation will therefore be very strong on both sides of the divide. Turnout might well be higher than, for example, in the 2015 general elections when it stood at 66% but it is unlikely to be as high as the 85% achieved in the 2014 Scottish independence referendum. What is less clear cut, however, is which camp a high turnout will benefit. On the one hand, the ‘leave’ side might be able to mobilise disaffected voters who do not tend to turn out in general elections. On the other hand, the core support for leaving the EU will likely be sufficiently mobilised to turn out anyway and will already be ‘priced into’ current opinion polls. An exceptionally high turnout at the referendum would therefore likely be driven by the mobilisation of supporters for staying in the EU and thus be to the benefit of the ‘remain’ camp.

Establishment vs anti-establishment

A distinctive feature of referendum campaigns is their binary and polarised nature. In the case of EU referendums, this generally pits the establishment on the pro-EU side against the anti-establishment on the Eurosceptic side. This binary structure tends to work as a magnifying glass for the anti-establishment case, and part of the resonance of Eurosceptic arguments in EU referendums precisely comes from their anti-establishment appeal. However, this divide between the establishment and critics of that establishment is probably less pronounced in the current British referendum than in many previous EU referendums across Europe. This is because the case for leaving the EU has moved towards the mainstream in British politics and resonates with parts of the political and economic establishment as well as across large swathes of the print media. At the same time, it is still evident that the ‘leave’ campaign seeks to play the anti-establishment card, trying to present itself as ‘outsiders’ standing up for the British people against Whitehall elites and ‘Brussels’.

Elite cues matter

Although party identification is a less important driver of voting behaviour in EU referendums than in general elections, cues from the elites still matter. In particular, such cues will be more powerful, the more united each of the two camps is and the more voters trust their leading figures. However, elite cues on both sides of the debate will likely be weakened by internal divisions. The ‘leave’ camp has difficulty finding a common line on how to engage with UKIP and on whether it should officially be led by ‘Vote Leave’ or ‘Leave.EU’. On the ‘remain’ side, the cues from the government to Conservative voters will become weaker the more the Conservative party and the cabinet are divided. In terms of trust, the ‘remain’ campaign appears to be on the advantage, because David Cameron is better trusted on the referendum in the public at large than any leading figure of the ‘leave’ campaign, including Boris Johnson. In particular, Nigel Farage divides public opinion and is trusted mainly by those who have already decided to vote for leaving the EU. His cues will thus be unlikely to sway many voters who are yet undecided.

Priming effects

Voters in EU referendums are primed to think about the question on the ballot in terms of the issues that are on the forefront of their minds on voting day. This suggests that the outcome of the referendum will be affected by which issues are most prominent in June. If the issue agenda at the time of the vote will still be dominated by immigration, crowding out, for example, economic arguments and concerns, voters will be primed to decide on EU membership in terms of what they think it implies for immigration. This stands to benefit the ‘leave’ side which should therefore be expected to focus their campaign on the immigration issue. The more the political debate at the time of the referendum reflects a more optimistic mood and a broad sense of satisfaction with the government and with personal circumstances, the more this should benefit the ‘remain’ side.

The Status quo and the consequences of leaving

Voting behaviour in referendums (and elsewhere) is marked by a bias in favour of the status quo. Voters tend to be risk averse and prefer the certainty of the status quo to the uncertainty of change. The riskier voters consider leaving the EU to be, the more this benefits the ‘remain’ side. Much of the referendum campaign will therefore become a framing contest about the consequences of voting to leave. While the ‘remain’ campaign will portray leaving the EU as – in David Cameron’s words – a ‘great leap into the dark’, economically and politically. The ‘leave’ campaign will make the case that change would be gradual and incremental and that leaving the EU would not entail a radical break with the past. The more dissatisfied voters are with the status quo and the more they believe to lose out from it, however, the more risk acceptant they will become and the more likely they will be prepared to vote against the status quo and for leaving the EU even if this is seen as risky.

This will be a tight referendum. The outcome is hard to predict but we can learn from other referendums. We can to some extent be aware of what we don’t know on turnout, on priming, elite cues and issue salience. These may well have a crucial effect in determining the outcome. But, of course, the other category that Rumsfeld has was the ‘unknown unknowns’, or as Macmlillan would have it, ‘events’. The key ‘known known’ we have is that the next few months will matter in determining the outcome of one of the momentous decisions in UK politics.