Questions raised about the relative wealth of an independent Scotland

With 16 weeks left until the vote, the official Scottish referendum campaign kicked off today with both 'yes' and 'no' camps hoping to convince any wavering voters.

The potential economic costs and benefits of an independent Scotland have provided the focus for much of the debate so far, and earlier this week the Treasury found itself under attack for allegedly "misrepresenting" the start-up costs for a new sovereign Scottish government.

Today it was the 'yes' camp's figures that were under scrutiny, with the Guardian reporting on its front page that "new doubt" had been cast over the Scottish government's claims about the relative wealth of an independent Scotland.

Scottish First Minister Alex Salmond has previously claimed that an independent Scotland would be the 14th richest country in the OECD group of developed economies. We've previously factchecked claims that placed Scotland as high as sixth on that list, and found a number of gaps in the figures.

The "new doubt" that has been cast on this claim comes in a paper published by researchers from Glasgow University, which points out these estimates rely on looking at Scotland's GDP per capita: the average amount of economic activity produced by someone living in Scotland.

While GDP is the basis for most international comparisons when it comes to the relative size of a country's economy, the researchers argue that it isn't necessarily a good measure of its wealth. This is because not all of the wealth produced by that economic activity necessarily ends up in the pockets of Scots. Where a country has a high proportion of foreign ownership of its key industries - which the researchers argue applies in Scotland's case - then much of the value created in Scotland is eventually transferred overseas.

Instead, they propose looking at Gross National Income (GNI), which is a measure of the money generated by Scottish citizens in a year. This is problematic, as GNI figures are currently only officially and regularly produced for the UK, and not its constituent parts.

However the researchers have looked at two estimates of GNI - one from the Scottish government and one of their own devising - and found that on this measure, Scotland's wealth per citizen is similar to the UK as a whole, and may even be slightly lower.

As the Guardian reports, looking at the figures this way also has the effect of making each Scot nearly £3,000 poorer than if GDP is used, and could see Scotland as low as 20th in the OECD 'wealth per capita' rankings.

A spokesperson for the Scottish government told the paper: "We use GDP per capita because it is the most commonly used and accepted measure of relative economic strength."