Alex Salmond has a woman problem and it might cost him the referendum. Just 27% of women plan to vote for Scottish independence, compared to 39% of men, according to Monday's Scottish Social Attitudes survey. That's a 12-point gender gap. It has doubled since last year and is the highest ever recorded in the survey.
It's at its peak, but the gap has been there for some time. The survey consistently found a gap of between six and seven points. The gender gap varies from pollster to pollster but they all find it – from just one per cent in July's ICM poll to 15 points in June's Panelbase's poll.
"The gap is consistent, it's been there for a very long time," Michael Keating, chair of Scottish Politics at the University of Aberdeen, says. "It's consistent with independence referendum polls in Quebec and Catalonia."
Women's nervousness about independence is a major issue for Salmond and Alistair Darling. Both sides have set up groups aiming to marshal the female vote – Women for Independence on one side and Better Together Women on the other. Salmond hoped that promises on childcare in the Scottish government's independence white paper might tip the scale. He was wrong.
Could it be Salmond himself? The Scottish first minister has long had a personal woman problem. Even after winning the Scottish parliament election in 2011, when his approval ratings were through the roof, he was significantly less popular with women than with men.
It doesn't appear so. His efforts to put his deputy Nicola Sturgeon front and centre of the campaign made no difference. The gender gap is still there among people who think he's doing a pretty good job. And it was there long ago too, before he was even leader. Salmond might not be helping matters, but it's certainly not all his fault.
More than any other factor, women's aversion to independence seems based on uncertainty. They are more nervous about what follows such a radical break with the status quo.
It's easy to misrepresent this trend. It does not necessarily mean women are more supportive of the union, but rather that they are less certain about what splitting from it would entail.
Fifty-two per cent of women say devolution is their preferred option, just a little higher than 48% of men. But women are much more likely to say they do not know which constitutional arrangement they prefer – by 15% compared to five per cent of men. They're also more likely to still be undecided, with 32% of women selecting this option, compared to 25% of men.
Women are also much more likely to express uncertainty about the consequences of independence. Nineteen per cent of women say they don't know if Scotland's economy will do better or worse.
Keating cites "caution, risk aversion and concern about social consequences of change" as key reasons for the gender gap.
John Curtice, professor of politics at the University of Strathclyde and one of Britain's leading election analyst, agrees.
"Women are more likely to feel uncertain about the consequences of independence and voters - regardless of whether they're men or women - are less likely to vote for independence if they feel uncertain about the consequences," he says.
"It's to do with women being more uncertain of what would happen as a result."
Women aren't just more uncertain about what would follow from independence. Regardless of whether they believe things will get better or worse, they are more uncertain about their opinion.
Just 27% of women said they are quite or very sure about what would follow independence, compared to 37% of men.
This is the key variable. That type of uncertainty is a major factor in support for independence. As Curtice reports, 96% of those who believe independence will improve the economy and are sure about it will vote 'Yes' in September. But among those who think it will improve the economy but are less certain, the figure drops to 72%.
Women do not have different policy priorities to men and they are not particularly being put off by Salmond. They are just more uncertain about the outcome of independence and therefore less likely to vote for change.
It is easy to explain this as women being more fearful than men; more risk-averse and cautious. But that would be misleading. As ever, women are being more sensible. The Scottish independence debate is fiendishly complex and hard to predict. In this debate, certainty may just be a form of naivety.
Even if Scotland votes yes, it is not clear precisely what it has voted for.
"The referendum in September isn't the final verdict on the matter. It's not going to be determinative of Scotland's political status," Jo Murkens, an expert in constitutional law at the London School of Economics (LSE), says.
"It just means negotiations will take place between Scotland and London where independence is discussed. All sorts of matters will be discussed - like Trident, national debt, the role of the Queen, the Post Office. Everything from high politics to low. The result of those negotiations is uncertain. Even the duration is uncertain.
"We can't predict which way it's going to go. So a lot of the debate has been a little bit irritating. We're presented with certainties: 'If Scotland becomes independent X will happen'. But whole point of a negotiation process is that these matters are to be discussed."
Perhaps women aren't being more fearful. Perhaps they're just better at seeing through politicians' bluster.