Statistic cited to defend austerity partially based on Excel error

How bad did Reinhart and Rogoff get it?

 

Reinhart and Rogoff

It's always hard to work out how much policy is based on actual evidence, rather than the preconceptions of politicians and policymakers, but if any research has had an effect, it's surely Carmen Reinhart and Ken Rogoff's 2009 book This Time it's Different. It's the source of a claim which has outgrown its roots, and come to be cited in policy debates worldwide: that growth drops precipitously if the ratio of debt to GDP rises above 90 per cent. But now, a new paper shows that that claim is partially the result of some astonishing oversight – including an error in the authors' Excel spreadsheet which excluded five countries from the analysis.

The book itself examines the link between the ratio of debt to GDP and growth rates in a raft of countries from World War II onwards. It finds that the higher the debt to GDP ratio, the lower real growth in those countries – and that there is a massive drop of debt to GDP ratios rise above 90 per cent, when the average growth rate becomes slightly negative.

To be fair to Reinhart and Rogoff (or R&R, as the cool kids do not say), the claim they make has been spun out of proportion by supporters keen to use it for political ends. The authors don't explicitly present the 90 per cent level as a cliff, just highlight what the data says; and they don't draw a causal inference, speaking, as they point out today, "of 'association' and not 'causality.'"

Herndon, Ash and Pollin

Even so, however, no other researcher has been able to replicate their "association", and no satisfactory explanation has been given as to why that is. Until now. The new critique, "Does High Public Debt Consistently Stifle Economic Growth? A Critique of Reinhart and Rogoff" by Thomas Herndon, Michael Ash and Robert Pollin (HAP, in economistspeak), is damning. It highlights three inaccuracies in R&R: "coding errors, selective exclusion of available data, and unconventional weighting of summary statistics".

Of those, the first is the most painful, albeit the least important. Reinhart and Rogoff simply added up their spreadsheet wrong. Mike Konczal's report on the paper illustrates the error: the blue box encloses the cells which R&R used to estimate the average; notice how it doesn't go all the way to the bottom? It should:

Missing out the last five rows – particularly Belgium, which had an average growth rate of 2.6 per cent during the years it had a debt to GDP ratio above 90 per cent – changes the average from -0.1 per cent to 0.2 per cent.

That error explains why no-one else could replicate R&R's findings – but the other two problems cast further doubt on whether even the 0.2 per cent figure is acceptable.

The HAP paper finds that R&R exclude certain years in certain countries for no documented reason. These include five years in which New Zealand has a debt to GDP ratio of over 90 per cent. With those years included, the average growth during New Zealand's six years above the threshold is 2.58 per cent; with them excluded it plummets to -7.6 per cent. Similar, albeit smaller, results are found for Australia and Canada, which are also excluded for short periods immediately after the war.

Finally, the HAP paper addresses the way in which R&R weight the results. Each country's data is averaged out, and then the average of those averages is found. That has the effect of valuing the 19 data points that the UK offers above 90 per cent debt/GDP – which average 2.4 per cent growth – with the same weight as the single year that New Zealand offers, when growth was -7.6 per cent.

With all the criticisms applied, the HAP paper reports that the average growth rate for years with a debt/GDP ratio is not -0.1 per cent, but 2.2 per cent. The steep drop-off at 90 per cent disappears; and the credibility of those who cited it should take a hit.

Reinhart and Rogoff Respond

But Reinhart and Rogoff aren't taking it sitting down. With an astonishing turnaround, they have issued a response – published at 3am Boston time – which addresses the critique.

They concede the Excel error – "full stop" – but give a defence for the other two points. The full data for the years excluded was not available when they did their research, they argue, and so while it may make sense to include now, they cannot be held responsible for its absence:

This charge, which permeates through their paper, is one we object to in the strongest terms. The “gaps” are explained by the fact there were still gaps in our public data debt set at the time of this paper.

They also defend the odd choice of weightings, saying that:

Our approach has been followed in many other settings where one does not want to overly weight a small number of countries that may have their own peculiarities.

That is, they argue that just because there is more data for Britain than New Zealand, that does not mean Britain should be weighed more strongly, since that runs the risk that its "peculiarities" might alter the result.

The problem is that neither approach is obviously preferable. While R&R have a point, so to do HAP – which leaves us in the position of questioning the viability of such analysis in the first place.

But R&R make one final defence:

[Herndon et al], too, find lower growth associated with periods when debt is over 90 per cent. Put differently, growth at high debt levels is a little more than half of the growth rate at the lowest levels of debt.

They published this table, via Business Insider, to make the claim clearer:

Does it even matter?

But here's the thing: Reinhart and Rogoff's claim that the HAP paper agrees with them is more evidence of the supreme obviousness of their associative claim. "A high ratio of debt to GDP is correlated with low growth in GDP" is not an interesting finding, it's as close to a mathematical truism as economic statements come. Reinhart and Rogoff's paper is only important insofar as people have read two things into it which aren't true: firstly, that high debt to GDP ratios cause low growth; and secondly, that there is a discontinuity at 90 per cent, where things get much, much worse.

Reinhart and Rogoff themselves disavow the first claim, writing that:

We are very careful in all our papers to speak of "association" and not "causality".

And the second claim has been put to bed by the Herndon et al paper. There is no major drop at 90 per cent, because that was an artefact of incomplete data, errors in coding, and an odd weighting system.

(Incedentally, the 90 per cent discontinuity was a red herring anyway, because it only exists due to the fact that R&R broke up their data into bands 30 percentage points wide. Anyone focusing too heavily on it as a "magic number" simply failed to read the methods section)

And so we are left in much the same place we were beforehand. There remains no evidence that high debt causes GDP growth to slow, rather than slow GDP growth causing high debt. And that lack of evidence will have precisely no effect on public debate, because it's basically all data-free anyway.

There is one change, though. The thesis that Excel is the most dangerous piece software in the world just got a massive boost.

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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Ken Livingstone says publicly what many are saying privately: tomorrow belongs to John McDonnell

The Shadow Chancellor has emerged as a frontrunner should another Labour leadership election happen. 

“It would be John.” Ken Livingstone, one of Jeremy Corbyn’s most vocal allies in the media, has said publicly what many are saying privately: if something does happen to Corbyn, or should he choose to step down, place your bets on John McDonnell. Livingstone, speaking to Russia Today, said that if Corbyn were "pushed under a bus", John McDonnell, the shadow chancellor, would be the preferred candidate to replace him.

Even among the Labour leader’s allies, speculation is rife as to if the Islington North MP will lead the party into the 2020 election. Corbyn would be 71 in 2020 – the oldest candidate for Prime Minister since Clement Attlee lost the 1955 election aged 72.

While Corbyn is said to be enjoying the role at present, he still resents the intrusion of much of the press and dislikes many of the duties of the party leader. McDonnell, however, has impressed even some critics with his increasingly polished TV performances and has wowed a few sceptical donors. One big donor, who was thinking of pulling their money, confided that a one-on-one chat with the shadow chancellor had left them feeling much happier than a similar chat with Ed Miliband.

The issue of the succession is widely discussed on the left. For many, having waited decades to achieve a position of power, pinning their hopes on the health of one man would be unforgivably foolish. One historically-minded trade union official points out that Hugh Gaitskell, at 56, and John Smith, at 55, were 10 and 11 years younger than Corbyn when they died. In 1994, the right was ready and had two natural successors in the shape of Tony Blair and Gordon Brown in place. In 1963, the right was unprepared and lost the leadership to Harold Wilson, from the party's centre. "If something happens, or he just decides to call it a day, [we have to make sure] it will be '94 not '63," they observed.

While McDonnell is just two years younger than Corbyn, his closest ally in politics and a close personal friend, he is seen by some as considerably more vigorous. His increasingly frequent outings on television have seen him emerge as one of the most adept media performers from the Labour left, and he has won internal plaudits for his recent tussles with George Osborne over the tax bill.

The left’s hopes of securing a non-Corbyn candidate on the ballot have been boosted in recent weeks. The parliamentary Labour party’s successful attempt to boot Steve Rotheram off the party’s ruling NEC, while superficially a victory for the party’s Corbynsceptics, revealed that the numbers are still there for a candidate of the left to make the ballot. 30 MPs voted to keep Rotheram in place, with many MPs from the left of the party, including McDonnell, Corbyn, Diane Abbott and John Trickett, abstaining.

The ballot threshold has risen due to a little-noticed rule change, agreed over the summer, to give members of the European Parliament equal rights with members of the Westminster Parliament. However, Labour’s MEPs are more leftwing, on the whole, than the party in Westminster . In addition, party members vote on the order that Labour MEPs appear on the party list, increasing (or decreasing) their chances of being re-elected, making them more likely to be susceptible to an organised campaign to secure a place for a leftwinger on the ballot.

That makes it – in the views of many key players – incredibly likely that the necessary 51 nominations to secure a place on the ballot are well within reach for the left, particularly if by-election selections in Ogmore, where the sitting MP, is standing down to run for the Welsh Assembly, and Sheffield Brightside, where Harry Harpham has died, return candidates from the party’s left.

McDonnell’s rivals on the left of the party are believed to have fallen short for one reason or another. Clive Lewis, who many party activists believe could provide Corbynism without the historical baggage of the man himself, is unlikely to be able to secure the nominations necessary to make the ballot.

Any left candidate’s route to the ballot paper runs through the 2015 intake, who are on the whole more leftwing than their predecessors. But Lewis has alienated many of his potential allies, with his antics in the 2015 intake’s WhatsApp group a sore point for many. “He has brought too much politics into it,” complained one MP who is also on the left of the party. (The group is usually used for blowing off steam and arranging social events.)

Lisa Nandy, who is from the soft left rather than the left of the party, is widely believed to be in the running also, despite her ruling out any leadership ambitions in a recent interview with the New Statesman.However, she would represent a break from the Corbynite approach, albeit a more leftwing one than Dan Jarvis or Hilary Benn.

Local party chairs in no doubt that the shadow chancellor is profiling should another leadership election arise. One constituency chair noted to the New Statesman that: “you could tell who was going for it [last time], because they were desperate to speak [at events]”. Tom Watson, Caroline Flint, Chuka Umunna, Yvette Cooper, Andy Burnham and Liz Kendall all visited local parties across the country in preparation for their election bids in 2015.

Now, speaking to local party activists, four names are mentioned more than any other: Dan Jarvis, currently on the backbenches, but in whom the hopes – and the donations – of many who are disillusioned by the current leadership are invested, Gloria De Piero, who is touring the country as part of the party’s voter registration drive, her close ally Jon Ashworth, and John McDonnell.

Another close ally of Corbyn and McDonnell, who worked closely on the leadership election, is in no doubt that the shadow chancellor is gearing up for a run should the need arise.  “You remember when that nice Mr Watson went touring the country? Well, pay attention to John’s movements.”

As for his chances of success, McDonnell may well be even more popular among members than Corbyn himself. He is regularly at or near the top of LabourList's shadow cabinet rankings, and is frequently praised by members. Should he be able to secure the nominations to get on the ballot, an even bigger victory than that secured by Corbyn in September is not out of the question.

Stephen Bush is editor of the Staggers, the New Statesman’s political blog. He usually writes about politics.