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.

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The Brexit select committee walkout is an ominous sign of things to come

Leavers walked out of a meeting of Hilary Benn's "gloomy" committee yesterday. Their inability to accept criticism could have disastrous consequences

“Hilary Benn isn’t managing a select committee. He’s managing an ecosystem.” That was the stark verdict of one member of the Commons' Brexit committee on its fitness for purpose yesterday. If its meeting on the eve of Article 50 is anything to go by, then Benn’s fragile biome might already be damaged beyond repair.

Unhappy with the content of its “gloomy” provisional 155-page report into the government’s Brexit white paper, leavers on the committee walked out of its meeting yesterday. The committee is a necessarily unwieldy creation and it would probably be unreasonable to expect it to agree unanimously on anything: it has 21 members where others have 11, so as to adequately represent Leavers, Remainers and the nations.

Disagreements are one thing. Debate and scrutiny, after all, are why select committees exist. But the Brexiteers’ ceremonial exodus augurs terribly for the already grim-looking trajectory of the negotiations to come. “As I understand it, they don’t like analysing the evidence that they have,” another pro-Remain member of the committee told me.

Therein lies the fundamental weakness of the Brexiteers’ position: they cannot change the evidence. As was the case with the 70 MPs who wrote to Lord Hall last week to accuse the BBC of anti-Brexit bias, they assume a pernicious selectivity on the part of Remainers and their approach to the inconvenient facts at hand. None exists.

On the contrary, there is a sense of resignation among some Remainers on the Brexit committee that their reports will turn out to be pretty weak beer as a consequence of the accommodations made by Benn to their Eurosceptic colleagues. Some grumble that high-profile Brexiteers lack detailed understanding of the grittier issues at play – such as the Good Friday Agreement – and only value the committee insofar as it gives them the opportunity to grandstand to big audiences.

The Tory awkward squad’s inability to accept anything less than the studied neutrality that plagued the Brexit discourse in the run-up to the referendum – or, indeed, any critical analysis whatsoever – could yet make an already inauspicious scenario unsalvageable. If they cannot accept even a watered-down assessment of the risks ahead, then what happens when those risks are made real? Will they ever accept the possibility that it could be reality, and not the Remain heretics, doing Britain down? How bad will things have to get before saving face isn’t their primary imperative?

Yesterday's pantomime exit might have been, as one committee member told me, “hysterically funny”. What’s less amusing is that these are the only people the prime minister deigns to listen to.

Patrick Maguire writes about politics and is the 2016 winner of the Anthony Howard Award.