The most important paragraph in the IMF World Economic Outlook

68 words of wonkishness.

The IMF's World Economic Outlook (pdf) – a 230-page tome detailing predictions on nearly every aspect of the world's economy collated by the international organisation – always gets attention for the calls it makes.

The October edition downgrades expected global growth for 2013 from 3.9 per cent to 3.6 per cent, and also cuts predictions for China (down to 8.2 per cent for 2013), the US (expected to grow by 2.1 per cent in 2013, down from 2.3 per cent in July's prediction) and the UK (now expected to grow by just 1.1 per cent next year, and to contract by 0.2 per cent this year).

But the predictions are not the most important passages in this edition of the Outlook. Those are found in a short box-out titled Are We Underestimating Short-Term Fiscal Multipliers?

The fisc§al multiplier is the effect government spending has on GDP. Money spent by the government doesn't disappear – it is respent, again and again. If a teacher gets a pay rise, their consumption is likely to rise in line with it; if all teachers get pay rises, that increase in consumption may be enough to affect the aggregate demand in the economy. In an economy which isn't being stretched to its limits – that is, one without full employment, or serious capital equipment shortages – that increase in aggregate demand will result in an increase in GDP.

The existence of the fiscal multiplier is a matter of fact, but the magnitude of it is contested. And that's where the IMF enters the scene, on page 42:

The main finding, based on data for 28 economies, is that the multipliers used in generating growth forecasts have been systematically too low since the start of the Great Recession, by 0.4 to 1.2, depending on the forecast source and the specifics of the estimation approach. Informal evidence suggests that the multipliers implicitly used to generate these forecasts are about 0.5. So actual multipliers may be higher, in the range of 0.9 to 1.7.

Emphasis mine. When deciding how much to spend, governments have been assuming that every pound they spend increases GDP by 50p – but it may increase it by as much as £1.70.

The reason this is so very important is that fiscal multiplier is usually appealed to not when deciding how much to spend, but how much to not spend. When governments are planning austerity packages, they have to be wary of the fact that large cuts to government spending will inevitably cause a decrease in output, and so they either have to be prepared to take that hit, or come up with a reason why slashing spending will cause an increase in output through some other mechanism.

That is easy enough to do if you are trying to account for a fiscal multiplier of 0.5: you can make the arguments, which Osborne and Cameron rehearsed repeatedly, that the public sector is crowding out the private; that the government spending which is being cut is particularly inefficient; or that the confidence fairies will reward your thriftiness with growth.

When there is the chance that the fiscal multiplier is three times that, austerity becomes much more likely to involve damaging drops in output.

There was once a time when the government pegged its credibility to that of the IMF – back when George Osborne was proud about Britain's credit ratings, and the international community was behind his plans. Those days are gone, and have been since Christine Lagarde made her own attack on austerity. But the economists at the treasury may be more inclined to listen to the wonkish findings of the World Outlook than the political interventions of the fund's leader. We can only hope they are prompted to re-do the sums.

The IMF headquarters. Photograph: Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

How Jim Murphy's mistake cost Labour - and helped make Ruth Davidson

Scottish Labour's former leader's great mistake was to run away from Labour's Scottish referendum, not on it.

The strange revival of Conservative Scotland? Another poll from north of the border, this time from the Times and YouGov, shows the Tories experiencing a revival in Scotland, up to 28 per cent of the vote, enough to net seven extra seats from the SNP.

Adding to the Nationalists’ misery, according to the same poll, they would lose East Dunbartonshire to the Liberal Democrats, reducing their strength in the Commons to a still-formidable 47 seats.

It could be worse than the polls suggest, however. In the elections to the Scottish Parliament last year, parties which backed a No vote in the referendum did better in the first-past-the-post seats than the polls would have suggested – thanks to tactical voting by No voters, who backed whichever party had the best chance of beating the SNP.

The strategic insight of Ruth Davidson, the Conservative leader in Scotland, was to to recast her party as the loudest defender of the Union between Scotland and the rest of the United Kingdom. She has absorbed large chunks of that vote from the Liberal Democrats and Labour, but, paradoxically, at the Holyrood elections at least, the “Unionist coalition” she assembled helped those parties even though it cost the vote share.

The big thing to watch is not just where the parties of the Union make gains, but where they successfully form strong second-places against whoever the strongest pro-Union party is.

Davidson’s popularity and eye for a good photo opportunity – which came first is an interesting question – mean that the natural benefactor in most places will likely be the Tories.

But it could have been very different. The first politician to hit successfully upon the “last defender of the Union” routine was Ian Murray, the last Labour MP in Scotland, who squeezed both the  Liberal Democrat and Conservative vote in his seat of Edinburgh South.

His then-leader in Scotland, Jim Murphy, had a different idea. He fought the election in 2015 to the SNP’s left, with the slogan of “Whether you’re Yes, or No, the Tories have got to go”.  There were a couple of problems with that approach, as one  former staffer put it: “Firstly, the SNP weren’t going to put the Tories in, and everyone knew it. Secondly, no-one but us wanted to move on [from the referendum]”.

Then again under different leadership, this time under Kezia Dugdale, Scottish Labour once again fought a campaign explicitly to the left of the SNP, promising to increase taxation to blunt cuts devolved from Westminster, and an agnostic position on the referendum. Dugdale said she’d be open to voting to leave the United Kingdom if Britain left the European Union. Senior Scottish Labour figures flirted with the idea that the party might be neutral in a forthcoming election. Once again, the party tried to move on – but no-one else wanted to move on.

How different things might be if instead of running away from their referendum campaign, Jim Murphy had run towards it in 2015. 

Stephen Bush is special correspondent at the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to British politics.

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