‘Yes’ campaign activist Lloyd Quinan paints campaign posters in an office in Edinburgh September 11, 2014.The referendum on Scottish independence will take place on September 18, when Scotland will vote whether or not to end the 307-year-old union with the rest of the United Kingdom. REUTERS/Paul Hackett

As part of our continuing series of Monkey Cage Election Reports, the following is a pre-election report on the coming Scottish Referendum on independence from Tom O’Grady, a Ph.D. student in political science at MIT.

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On Sept. 18, Scottish voters will take part in a referendum asking one simple question: “Should Scotland be an independent country?” Until recently, the consensus amongst politicians and pollsters alike was that the Scots would say “no, thanks” — to use the favorite slogan of the anti-independence “Better Together” campaign. All year, polls have given the “no” camp leads of at least 10 percent. But this week everything changed. A shock opinion poll published Sept. 7 gave independence a 2 percent lead. Other polls have confirmed a substantial narrowing of the race to essentially a statistical dead heat, although overall the “no” camp seems to have a slight edge. The British media is suddenly filled with articles on the practicalities of independence. Would a passport be needed to cross the Scottish-English border, for instance?

Whether due to a sentimental attachment to the idea of a United Kingdom or cold electoral necessity, the main British parties all oppose independence. In recent days, they have been falling over themselves to offer concessions in the hope of winning over wavering “yes” voters. Scots are now promised that their parliament, currently considerably less powerful than U.S. state governments, would be beefed up in the event of a “no” vote. New tax-raising powers would arrive, together with responsibility for an array of new policy areas. The United Kingdom as a whole would probably adopt an essentially federal system of government. Whatever the ultimate result, the pro-independence Scottish National Party looks set to achieve far greater power for Scotland, and the United Kingdom is going to change irrevocably.

This watershed vote raises two questions for political scientists. First, what will happen next week? And second, why has the independence campaign achieved such success? The simple answer to the first question is that it’s extraordinarily hard to predict. Turnout in the referendum is likely to be unprecedented. About 85 percent of Scots claim they will definitely vote next week; only 50 percent did so in the last Scottish parliament election. Pollsters usually apply weightings to their results, so that the random sample they obtain looks more like the voting population at large. This includes weighting the sample according to respondents’ past votes. But here, there are no previous referenda offering guidance to pollsters, and a large proportion of those voting may never have voted before.

To make things worse, pre-election surveys may be biased when one side is more fashionable or stigmatized than the other. British pollsters are still haunted by the 1992 general election. They widely predicted a win for the Labor party, only to see the Conservatives (Tories) squeeze into power. Pollsters blamed a phenomenon they called the “Shy Tory” effect. The Tories were seen as deeply unfashionable, even incompetent, after 13 years in power. Some survey respondents were unwilling to admit that they planned to support them. In Scotland today, voting “yes” arguably seems the more glamorous and patriotic option. As a result, “Shy Unionists” may lead pollsters to under-estimate opposition to independence.

But there is also the well-known “Bradley Effect,” where survey respondents are unwilling to admit that they will vote against black politicians. It can lead pollsters to paint too rosy a picture of support for black candidates. Recent research claims that when blacks become more stigmatized in national discourse, voters become more reluctant to admit their true hostility to pollsters. It may be that they fear being judged as racist. In Scotland, separatist rhetoric has become deeply entwined with opposition to the U.K.’s Conservative government, and there is certainly a small but vocal anti-English fringe amongst independence supporters. Thus voters may shy away from admitting support for independence, not wanting to be seen as anti-English. Ultimately, whether the polls are biased in one direction depends on which group is more numerous: “shy unionists” or “bradley” voters.

While these studies on public opinion and voting suggest great caution in predicting the result, past referendum campaigns offer most hope to the no side. Perhaps the most important finding in the literature on referenda is a clear status quo bias. For example, a famous study of Quebec’s 1995 independence referendum found that some voters placed heavy emphasis on the “worst possible outcome,” helping shore up support at the last minute for remaining in Canada, when the Quebecois looked set to vote for separation. Opponents of Scottish independence are banking on a similar reaction there, stressing the economic difficulties an independent Scotland might face. These include questions of what currency it would use, and how its important banking sector would survive.

Nonetheless, a substantial number of voters don’t seem to weigh up the costs and benefits in referendum voting. Party politics matters, and the question of Scottish independence has become deeply partisan. This is the key to answering my second question: why has separation proved so popular?

The Conservative party, in power in London, has virtually no support in Scotland. Its pro-austerity policies are deeply unpopular amongst the more progressive Scottish electorate. In addition, Alex Salmond, the leader of the Scottish National Party, is far more popular than the pro-union leaders. This suggests two linked explanations for the popularity of independence. First, political science research tells us that when faced with a complex issue such as independence, voters often simply adopt the policies favored by their own party. This cue-taking is a shortcut, helping voters understand how people like them should approach a question. So there is probably an element of follow-my-leader in support for independence.

Second, the referendum has arguably ceased to be about independence at all. The Scottish National Party has framed independence as an opportunity for Scotland to enact a more liberal set of policies, ending forever the prospect of Tory rule. In doing so, it has assembled an unusual coalition in support of separation. When we think of nationalism, we often imagine older voters predominating, as well as opposition to immigration as a rallying factor. And, sure enough, support for independence is much lower amongst the young in Quebec. Yet, in contrast, support for Scottish independence is heavily skewed to the young. It is also much stronger among working-class voters. And Scottish nationalism is certainly not rooted in anti-immigrant sentiment: the Scottish National Party say that an independent Scotland would actually increase immigration. Arguably, the pro-independence coalition looks much like the types of groups that are rejecting conventional politics in Europe today more broadly. Younger and poorer voters show lower turnout in elections, are more likely to vote for anti-establishment fringe parties, and are scornful of traditional political elites. Overall, the Scottish National Party’s success has come partly from framing independence as a form of anti-establishment protest, as well as the sheer luck of holding a referendum that coincides with a Conservative government in the United Kingdom.

This means, though, that support for independence could ultimately prove fragile.

Political scientist Mark Beissinger has argued that participation in separatist movements often occurs for reasons that are far more prosaic than the rhetoric of its leaders suggests, and that it is often rational for separatist leaders to build coalitions that are mainly based on shared opposition to incumbents. The Scottish National Party seem to have cottoned on. Beissinger shows that in Ukraine’s Orange Revolution, a sudden fervor for democracy cannot explain much of the protest activity. Opposition to the incumbents primarily united protesters. In Ukraine’s case, the ambivalence of many pro-change demonstrators ultimately made Ukraine’s nascent democracy very fragile. It is not hard to see parallels to Scotland. As polling day approaches, voters who have been primarily mobilized on party political grounds may begin to doubt their commitment to independence.

Overall, a narrow “no” vote seems the most likely outcome. The fragility of Salmond’s coalition, combined with the pervasive effect of status-quo bias, will probably be enough to keep Scotland in the union. But with so many first-time voters, next Thursday will definitely be “squeaky bum time” for both sides of the debate, as well as the beginning of historic changes to the British political system.