DID First Minister Nicola Sturgeon get her sums wrong when she put forward an alternative to Westminster’s austerity agenda ... and does it make any difference if she did?

The Treasury certainly thinks she made a mistake.

It costed measures the Scottish First Minister laid out in a speech in February, in which she argued for a more gradual approach to cutting the UK Government’s deficit and debt.

Sturgeon suggested that, even if departmental spending was increased by 0.5% per year in real terms in the next parliament, debt would still FALL as a percentage of GDP from 2015/16 onwards.

The Treasury costings, on the contrary, suggest debt as a percentage of GDP under the Sturgeon proposal would GROW in the first two years of the parliament and then begin falling in 2018/19 from 82.2% to 81.4% in 2019/20.

It would still appear, though, that Sturgeon is justified in saying that the debt to GDP ratio could fall even if real term departmental spending is increasing, although the speed of this fall is not as rapid as she suggested, and the debt to GDP at the end of the parliament is fractionally higher than at the beginning (81.1%).

The reason for the differences between the Sturgeon and Treasury costings appear to be driven largely by assumptions about how the additional borrowing adds to debt interest repayments.

Ultimately, however, it is difficult to ascertain exactly the extent to which different assumptions made by each ‘side’ are driving the result.

The SNP does not appear to have produced an exposition of their analysis, while the Treasury analysis could certainly be more transparent (an attempt to replicate their figures requires cross-referencing various tables and debt ready reckoners published by the Office for Budget Responsibility (OBR), the interpretation of which can be ambiguous.

This all poses a number of questions.

First, does it make sense for the Treasury to cost opposition party policy? There would seem to be a stronger case for this role to be undertaken by an independent body. But George Osborne previously ruled out the idea of the OBR performing this role.

Second, how meaningful is it to use the Autumn Statement as the baseline against which the Sturgeon proposals are assessed? As has been pointed out by the Institute for Fiscal Studies, the fiscal tightening implied by the Autumn Statement is stronger than that proposed by any of the main UK parties, including the Conservatives.

Third, and most importantly, how significant is the difference between the estimated debt/GDP ratio under the Sturgeon plans made by the Treasury (81%) with that suggested by Sturgeon (79%)?

Arguably, this is a fairly minor difference. In both cases, the debt/GDP ratio remains high in the context of the period since the 1970s.

But whether the ratio is 79% or 81% doesn’t undermine the general point that Sturgeon was making.

With growth remaining lacklustre, economic output below potential, and with interest rates at the Zero Lower Bound, there is a strong argument for saying that now is not the right time to pursue rapid austerity.

Instead, use fiscal policy to help stimulate demand, and pursue austerity when interest rates can be reduced to offset the negative effect of austerity on demand.

Both sides could improve the transparency of their policy costings. But Sturgeon’s case for a slower path of deficit reduction is not undermined by splitting hairs on whether debt:GDP might be 79% or 81% in five years time.

David Eiser is a Research Fellow at the Centre on Constitutional Change and the University of Stirling