If the other party leaders could bottle what Nicola Sturgeon has got, they surely would.

She barely had time to settle into the role of First Minister before being plunged into this general election battle, yet she seems to be sailing through a campaign which is plainly taking its toll on several of her rivals.

Now information from focus groups is beginning to explain why voters are apparently responding so favourably to the party and its leader.

A number of factors appear to be contributing. Ms Sturgeon's relative newness is an advantage. She is seen as different from the other party leaders, and has not had to spend too much time defending a record which is far from convincing on some key issues including the Scottish Government's stewardship of education and the NHS.

Voters, women in particular, who disliked Alex Salmond, find Ms Sturgeon more palatable than her predecessor.

In fact, the SNP benefits from its experience of government, overcoming the fear factor for many voters. Many appear unsure about the specifics of the Scottish Government's policy responsibilities. but this merely adds to her Teflon qualities.

The referendum was a factor too, the findings suggest. By putting the SNP on an equal footing with national parties it has become a credible alternative for those dissatisfied with the other main parties.

Meanwhile Labour struggles to be a credible alternative itself, according to those contemplating switching from the party to the SNP.

Any sensible analysis of the rival manifestos would show the perception that Labour is 'no different' from the Tories to be untrue, but the Labour campaign seems to have failed to get this message across in Scotland, leaving many Labour voters less concerned about another Conservative government.

The independence referendum may also have given Scottish voters a taste for being at the heart of national debate and the general election campaign has certainly maintained that.

There is an emotional element to SNP support, which the focus groups have also picked up on. Not all its supporters have a clear perception of the party's policies, beyond an expectation that the party would stand up for Scotland. But notably, voters appear to feel they can vote for the SNP without it being an endorsement of independence despite the SNP's rivals talking up fears of a second referendum.

One remarkable element of all this, though, is the significance of Ms Sturgeon's own personal popularity. How many of those who hope for a Sturgeon-Miliband alliance in less than a week's time appreciate that Scotland's first minister is not standing in this election? Do those who disliked Alex Salmond realise that it is he, along with the SNP's Westminster leader Angus Robertson who will be attempting to shake up the UK parliament, should the polls prove correct, after the results come in?

In many ways the SNP's campaign has relied on an audacious sleight of hand in this respect. Ms Sturgeon's personal success in this campaign makes this a threat as well as an opportunity. If her party fulfils polling predictions on Friday, it will be important to ensure voters do not feel they have been misled.