ONS reports that ONS actually quite good at estimating GDP

Estimates rarely change that much, but have got worse since the crash.

A new study by the ONS (pdf) on the practice of revising quarterly GDP reveals that, despite some high-profile revisions, they are actually doing pretty well.

The current practice for GDP figures is to release a preliminary estimate 25 days after the quarter ends, then update it for a second estimate a month later, and release a final estimate shortly before the next quarter ends – before starting the whole process again. Even after the "final" estimate is made, there's the possibility of still more releases:

As further data become available there are potential revisions to the quarterly GDP figures in subsequent QNA releases, as well as in the annual national accounts Blue Book publication.

The Blue Book process enables annual data to be balanced at a much more detailed level and is also the opportunity for major methodological changes to be introduced.

Whenever the preliminary estimate delivers surprising news – as it did with the most recent results – there is always a rush to point out that these estimates are usually revised (as indeed they are). But the overall picture remains remarkably accurate. The following chart compares the GDP growth given in the initial estimate to the final estimate given five years later.


There are some pretty large changes month-to-month, but only one revision in the last 20 years which changed the big picture in any substantial way (the near-collapse in growth in early 1998 actually appears not to have occurred).

Even when the whole period is covered, the authors conclude:

In broad terms the picture of growth in GDP over the period from 1961 to 2012 quarter two is similar, irrespective of the maturity of data, although there are some exceptions. In particular the differences caused by revisions in the late 1980s were previously discussed in Brown et al, where a period of consistent upward revisions led to the Pickford Review (1989). The review implemented a number of methodological changes including the publication of a single measure of GDP.

But what about the most recent period of recession and recovery?Has the ONS got worse at making those initial estimates due to the changed economic circumstances?


The below chart shows the absolute revisions to GDP estimates in the first two years. The Pickford review of 1989, which changed the methodology substantially, clearly worked, reducing the mean revision from a change of at least 0.5 points to one of barely 0.2 points. But while there was a period of unprecedented accuracy in the late 1990s and early 2000s, things have got marginally worse recently – even while staying significantly better than they had been two decades before.


As a result, the review concludes that:

There is some evidence that in the latest periods, the size of revision has increased [although not significantly]. . .

It is possible that the assumptions and methods underpinning the early estimates of GDP may not be as robust in periods of greater volatility or at turning points in the economy as they were during the long period of stability from 1992 to 2007.

The most important thing to note, however, is that there is no significant trend for the direction of the revision. Although it's usually positive, it hasn't been recently:


So if you are hoping that a GDP estimate will be revised, be careful what you wish for – it may not go the way you hope.

GDP percentage growth, quarter on same quarter 1 year ago - estimates.

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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I'm far from convinced by Cameron's plans for Syria

The Prime Minister has a plan for when the bombs drop. But what about after?

In the House of Commons today, the Prime Minister set out a powerful case for Britain to join air strikes against Isil in Syria.  Isil, he argued, poses a direct threat to Britain and its people, and Britain should not be in the business of “outsourcing our security to our allies”. And while he conceded that further airstrikes alone would not be sufficient to beat Isil, he made the case for an “Isil first” strategy – attacking Isil now, while continuing to do what we can diplomatically to help secure a lasting settlement for Syria in which Assad (eventually) plays no part.

I agreed with much of David Cameron’s analysis. And no-one should doubt either the murderous barbarism of Isil in the region, or the barbarism they foment and inspire in others across the world.  But at the end of his lengthy Q&A session with MPs, I remained unconvinced that UK involvement in airstrikes in Syria was the right option. Because the case for action has to be a case for action that has a chance of succeeding.  And David Cameron’s case contained neither a plan for winning the war, nor a plan for winning the peace.

The Prime Minister, along with military experts and analysts across the world, concedes that air strikes alone will not defeat Isil, and that (as in Iraq) ground forces are essential if we want to rid Syria of Isil. But what is the plan to assemble these ground forces so necessary for a successful mission?  David Cameron’s answer today was more a hope than a plan. He referred to “70,000 Syrian opposition fighters - principally the Free Syrian Army (FSA) – with whom we can co-ordinate attacks on Isil”.

But it is an illusion to think that these fighters can provide the ground forces needed to complement aerial bombardment of Isil.  Many commentators have begun to doubt whether the FSA continues to exist as a coherent operational entity over the past few months. Coralling the myriad rebel groups into a disciplined force capable of fighting and occupying Isil territory is a heroic ambition, not a plan. And previous efforts to mobilize the rebels against Isil have been utter failures. Last month the Americans abandoned a $500m programme to train and turn 5,400 rebel fighters into a disciplined force to fight Isil. They succeeded in training just 60 fighters. And there have been incidents of American-trained fighters giving some of their US-provided equipment to the Nusra Front, an affiliate of Al Qaeda.

Why has it proven so hard to co-opt rebel forces in the fight against Isil? Because most of the various rebel groups are fighting a war against Assad, not against Isil.  Syria’s civil war is gruesome and complex, but it is fundamentally a Civil War between Assad’s forces and a variety of opponents of Assad’s regime. It would be a mistake for Britain to base a case for military action against Isil on the hope that thousands of disparate rebel forces can be persuaded to change their enemy – especially when the evidence so far is that they won’t.

This is a plan for military action that, at present, looks highly unlikely to succeed.  But what of the plan for peace? David Cameron today argued for the separation of the immediate task at hand - to strike against Isil in Syria – from the longer-term ambition of achieving a settlement in Syria and removing Assad.  But for Isil to be beaten, the two cannot be separated. Because it is only by making progress in developing a credible and internationally-backed plan for a post-Assad Syria that we will persuade Syrian Sunnis that fighting Isil will not end up helping Assad win the Civil War.  If we want not only to rely on rebel Sunnis to provide ground troops against Isil, but also provide stable governance in Isil-occupied areas when the bombing stops, progress on a settlement to Syria’s Civil War is more not less urgent.  Without it, the reluctance of Syrian Sunnis to think that our fight is their fight will undermine the chances of military efforts to beat Isil and bring basic order to the regions they control. 

This points us towards doubling down on the progress that has already been made in Vienna: working with the USA, France, Syria’s neighbours and the Gulf states, as well as Russia and Iran. We need not just a combined approach to ending the conflict, but the prospect of a post-war Syria that offers a place for those whose cooperation we seek to defeat Isil. No doubt this will strike some as insufficient in the face of the horrors perpetrated by Isil. But I fear that if we want not just to take action against Isil but to defeat them and prevent their return, it offers a better chance of succeeding than David Cameron’s proposal today. 

Stewart Wood is a former Shadow Cabinet minister and adviser to Ed Miliband. He tweets as @StewartWood.