Female voters are still showing a consistent lead for no, while overall turnout is expected to rise above 80%

If the referendum on Scottish independence were a normal election we probably wouldn't say, based on current polls, that the outcome of Thursday's vote was too close to call. Of five polls released in the final 24 hours of the campaign, four had the no vote ahead by four points, one by two points. Sixteen polls have so far been released this month and 14 of these polls have shown no in the lead.

Two days before the 2012 presidential election in France, an Ifop poll for Paris Match put the gap between François Hollande and Nicolas Sarkozy at four points. Nobody argued that that election was too close to call; rather Hollande was seen as the clear favourite. The polling was born out by events: he won the election by 3.5 points.

But the difference between the French election and the Scottish referendum is that France holds presidential elections regularly while the independence vote is a one-off or rare event. The absence of historical precedents contributes a higher degree of uncertainty.

While it's clear the no lead has shrunk, the underlying trends behind this movement appear to have stabilised in the past week. Above all, female voters are still showing a consistent and important lead for no.

A three-point gap may sound small, but as the votes mount up the margin of difference may become insurmountable before some of the big cities declare. The Press Association anticipates that Edinburgh, Glasgow and Aberdeen, which together are home to about 25% of registered voters, will be the last three councils to announce results on Friday morning, between 5am and 6am.

If Edinburgh were to declare and one side or the other were to be three points ahead with only Glasgow and Aberdeen remaining, the side in second place would need to win an unlikely 60% of the votes in Glasgow on a constant turnout to even up the race.

Should that three-point lead be maintained after Glasgow declares, then any Aberdeen result would quite probably be irrelevant to the outcome. In other words, a referendum is not like football where a three-point gap can be turned around in one game.

A difference of one more percentage point would have a more profound impact. Should one side or the other have a lead of at least four points before Edinburgh, Glasgow and Aberdeen declare, then unlikely results would need to emerge in the three big cities for the trailing side to win.

The one uncertainty remains turnout. Polls have asked respondents how sure they are of voting in the referendum. Based on these responses, a turnout well in excess of 80% is expected on Thursday. This would be considerably higher than in any recent election. As a comparison, at the 2010 general election turnout was 63.8% across Scotland and below 50% in parts of Glasgow – and it is extremely difficult to analyse the behaviour of those who have never voted or haven't done so in a long time.

Because of this all the polls could be systematically incorrect. In the 2011 AV referendum there were noticeable differences between polls, and some did better than others – but in the Scottish case, the pollsters would almost all need to be inaccurate. That's possible, but it is unlikely.

Betting markets say there's about an 80% chance of a no win. But if you were told there was a 20% chance of rain, you would probably carry an umbrella.