They have become an established part of the political landscape, even if old hands will tell you that the only poll that matters is when the electorate actually cast their vote.

Nonetheless, prepare to be bombarded with the findings of opinion surveys as the various sides in the independence debate extrapolate results from the views of, typically, 1000 people to represent the nation as a whole.

Here, we show you two poll-of-poll graphs. They depict long-term trends on two questions - are we for or against independence; and what do we think if a third option is added - of extra powers for Holyrood, but remaining as part of the UK. Earlier this year the question that will appear on the ballot paper was finalised: should Scotland be an independent country? There will be no "third" question about extending powers to Holyrood from Westminster.

Our other main disclaimer is that the various polling organisations - TNS BMRB/System Three, YouGov, ICM, Ipsos Mori, Survation - all ask their questions in slightly different ways, not least because some polls may have been commissioned by the parties themselves. We've also eliminated such variables as the "don't knows", whether all the sample are certain to vote, and how many people were polled.

So, rather than focussing on an individual poll, what matters is the picture over the years on the two issues as the debate continues. We'll update our graphs as the polls are carried out to let you see the trends develop.

FOR/AGAINST INDEPENDENCE




Since the 2003 Holyrood election, a large number of polls have been taken to gauge Scotland's view on independence. A small number suggest a majority favour full independence but, even SNP campaigners will concede, the trend up to now has been running in favour of remaining within the UK. Since 2008, the margin varies from -1 point (which is barely statistically valid) to 20+ points, but the pattern is there. Which is why the campaign between now and the referendum is so important for both sides.

EXTRA POWERS

To complicate matters, the Scottish people have previously indicated they would prefer not to have a simple either-or question on the ballot paper, with a significant if disparate group arguing that there should be a third option - devolving extra powers from London to Edinburgh. The mechanics of that devolution - and indeed how that question should be posed - were and are still the subject of much wrangling, but the pollsters have detected large-scale popular support, around two-thirds at the latest count. Earlier this year, a third question was ruled out - the question on the ballot paper will have a simple yes/no format. Our graphs show that, over polls since 1999, extra powers has regularly been the most favoured option, ahead of both independence and the status quo. And that's why the mainstream politicians argued so fiercely over the referendum choices: ostensibly to reflect democratic wishes, but with a close eye on how a third option would impact on the either-or question.