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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I believe only Yvette Cooper has the breadth of support to beat Jeremy Corbyn

All the recent polling suggests Andy Burnham is losing more votes than anyone else to Jeremy Corbyn, says Diana Johnson MP.

Tom Blenkinsop MP on the New Statesman website today says he is giving his second preference to Andy Burnham as he thinks that Andy has the best chance of beating Jeremy.

This is on the basis that if Yvette goes out first all her second preferences will swing behind Andy, whereas if Andy goes out first then his second preferences, due to the broad alliance he has created behind his campaign, will all or largely switch to the other male candidate, Jeremy.

Let's take a deep breath and try and think through what will be the effect of preferential voting in the Labour leadership.

First of all, it is very difficult to know how second preferences will switch. From my telephone canvassing there is some rather interesting voting going on, but I don't accept that Tom’s analysis is correct. I have certainly picked up growing support for Yvette in recent weeks.

In fact you can argue the reverse of Tom’s analysis is true – Andy has moved further away from the centre and, as a result, his pitch to those like Tom who are supporting Liz first is now narrower. As a result, Yvette is more likely to pick up those second preferences.

Stats from the Yvette For Labour team show Yvette picking up the majority of second preferences from all candidates – from the Progress wing supporting Liz to the softer left fans of Jeremy – and Andy's supporters too. Their figures show many undecideds opting for Yvette as their first preference, as well as others choosing to switch their first preference to Yvette from one of the other candidates. It's for this reason I still believe only Yvette has the breadth of support to beat Jeremy and then to go on to win in 2020.

It's interesting that Andy has not been willing to make it clear that second preferences should go to Yvette or Liz. Yvette has been very clear that she would encourage second preferences to be for Andy or Liz.

Having watched Andy on Sky's Murnaghan show this morning, he categorically states that Labour will not get beyond first base with the electorate at a general election if we are not economically credible and that fundamentally Jeremy's economic plans do not add up. So, I am unsure why Andy is so unwilling to be clear on second preferences.

All the recent polling suggests Andy is losing more votes than anyone else to Jeremy. He trails fourth in London – where a huge proportion of our electorate is based.

So I would urge Tom to reflect more widely on who is best placed to provide the strongest opposition to the Tories, appeal to the widest group of voters and reach out to the communities we need to win back. I believe that this has to be Yvette.

The Newsnight focus group a few days ago showed that Yvette is best placed to win back those former Labour voters we will need in 2020.

Labour will pay a massive price if we ignore this.

Diana Johnson is the Labour MP for Hull North.