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?

Maybe.

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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The rise of the green mayor – Sadiq Khan and the politics of clean energy

At an event at Tate Modern, Sadiq Khan pledged to clean up London's act.

On Thursday night, deep in the bowls of Tate Modern’s turbine hall, London Mayor Sadiq Khan renewed his promise to make the capital a world leader in clean energy and air. Yet his focus was as much on people as power plants – in particular, the need for local authorities to lead where central governments will not.

Khan was there to introduce the screening of a new documentary, From the Ashes, about the demise of the American coal industry. As he noted, Britain continues to battle against the legacy of fossil fuels: “In London today we burn very little coal but we are facing new air pollution challenges brought about for different reasons." 

At a time when the world's leaders are struggling to keep international agreements on climate change afloat, what can mayors do? Khan has pledged to buy only hybrid and zero-emissions buses from next year, and is working towards London becoming a zero carbon city.

Khan has, of course, also gained heroic status for being a bête noire of climate-change-denier-in-chief Donald Trump. On the US president's withdrawal from the Paris Agreement, Khan quipped: “If only he had withdrawn from Twitter.” He had more favourable things to say about the former mayor of New York and climate change activist Michael Bloomberg, who Khan said hailed from “the second greatest city in the world.”

Yet behind his humour was a serious point. Local authorities are having to pick up where both countries' central governments are leaving a void – in improving our air and supporting renewable technology and jobs. Most concerning of all, perhaps, is the way that interest groups representing business are slashing away at the regulations which protect public health, and claiming it as a virtue.

In the UK, documents leaked to Greenpeace’s energy desk show that a government-backed initiative considered proposals for reducing EU rules on fire-safety on the very day of the Grenfell Tower fire. The director of this Red Tape Initiative, Nick Tyrone, told the Guardian that these proposals were rejected. Yet government attempts to water down other EU regulations, such as the energy efficiency directive, still stand.

In America, this blame-game is even more highly charged. Republicans have sworn to replace what they describe as Obama’s “war on coal” with a war on regulation. “I am taking historic steps to lift the restrictions on American energy, to reverse government intrusion, and to cancel job-killing regulations,” Trump announced in March. While he has vowed “to promote clean air and clear water,” he has almost simultaneously signed an order to unravel the Clean Water Rule.

This rhetoric is hurting the very people it claims to protect: miners. From the Ashes shows the many ways that the industry harms wider public health, from water contamination, to air pollution. It also makes a strong case that the American coal industry is in terminal decline, regardless of possibile interventions from government or carbon capture.

Charities like Bloomberg can only do so much to pick up the pieces. The foundation, which helped fund the film, now not only helps support job training programs in coal communities after the Trump administration pulled their funding, but in recent weeks it also promised $15m to UN efforts to tackle climate change – again to help cover Trump's withdrawal from Paris Agreement. “I'm a bit worried about how many cards we're going to have to keep adding to the end of the film”, joked Antha Williams, a Bloomberg representative at the screening, with gallows humour.

Hope also lies with local governments and mayors. The publication of the mayor’s own environment strategy is coming “soon”. Speaking in panel discussion after the film, his deputy mayor for environment and energy, Shirley Rodrigues, described the move to a cleaner future as "an inevitable transition".

Confronting the troubled legacies of our fossil fuel past will not be easy. "We have our own experiences here of our coal mining communities being devastated by the closure of their mines," said Khan. But clean air begins with clean politics; maintaining old ways at the price of health is not one any government must pay. 

'From The Ashes' will premiere on National Geograhpic in the United Kingdom at 9pm on Tuesday, June 27th.

India Bourke is an environment writer and editorial assistant at the New Statesman.

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