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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Not since the Thatcher years have so many Tory MPs been so motivated by self-interest

Assured of an election win, backbenchers are thinking either advancing up the greasy pole, or mounting it for the first time. 

One hears despair from Labour not just about probable defeat, but from MPs who felt they had three years to improve the party’s fortunes, or to prepare for personal oblivion. In the Conservative Party, matters seem quite the opposite. Veterans of the 1983 election recall something similar: a campaign fought in the absolute certainty of winning. Theresa May talked of putting the interests of the country first when she engineered the poll, and one must believe she was sincere. However, for those expecting to be Tory MPs after 8 June there are other priorities. Theirs is not a fight for the national interest, because that for them is a foregone conclusion. It is about their self-interest: either advancing up the greasy pole, or mounting it for the first time. They contemplate years ahead in which to consolidate their position and, eventually, to shape the tone and direction of the party.

The luxury of such thoughts during a campaign comes only when victory is assured. In 1983 I worked for a cabinet minister and toured marginal seats with him. Several candidates we met – most of whom won – made it clear privately that however important it was to serve their constituents, and however urgent to save the country from the threats within what the late Gerald Kaufman later called “the longest suicide note in history”, there was another issue: securing their place in the Thatcher revolution. Certain they and their party would be elected in the aftermath of the Falklands War, they wanted their snout in the trough.

These are early days, but some conver­sations with those heading for the next House of Commons echo the sentiments of 1983. The contemporary suicide note has not appeared, but is keenly awaited. Tories profess to take less notice of opinion polls than they once did – and with good reason, given the events of 2015 and 2016 – but ­imagine their party governing with a huge majority, giving them a golden opportunity to advance themselves.

Labour promises to change the country; the Liberal Democrats promise to force a reconsideration of Brexit; Ukip ­promises to ban the burqa; but the Tories believe power is theirs without the need for elaborate promises, or putting any case other than that they are none of the above. Thus each man and woman can think more about what the probability of four or five further years in the Commons means to them. This may seem in poor taste, but that is human nature for you, and it was last seen in the Labour Party in about 2001.

Even though this cabinet has been in place only since last July, some Tory MPs feel it was never more than an interim arrangement, and that some of its incumbents have underperformed. They expect vacancies and chances for ministers of state to move up. Theresa May strove to make her team more diverse, so it is unfortunate that the two ministers most frequently named by fellow Tories as underachievers represent that diversity – Liz Truss, the Lord Chancellor, who colleagues increasingly claim has lost the confidence of the judiciary and of the legal profession along with their own; and Sajid Javid, the Communities Secretary, whom a formerly sympathetic backbencher recently described to me as having been “a non-event” in his present job.

Chris Grayling, the Transport Secretary, was lucky to survive his own stint as lord chancellor – a post that must surely revert to a qualified lawyer, with Dominic Grieve spoken of in that context, even though, like all ardent Remainers in the government, he would be expected to follow the Brexit line – and the knives are out for him again, mainly over Southern Rail but also HS2. David Gauke, the Chief Secretary to the Treasury, and the little-known Ben Gummer, a Cabinet Office minister, are tipped for promotion with Grieve if vacancies arise: that all three are white men may, or may not, be a consideration.

Two other white men are also not held in high regard by colleagues but may be harder to move: Boris Johnson, whose conduct of the Foreign Office is living down to expectations, and Michael Fallon, whose imitation of the Vicar of Bray over Brexit – first he was for it, then he was against it, and now he is for it again – has not impressed his peers, though Mrs May considers him useful as a media performer. There is also the minor point that Fallon, the Defence Secretary, is viewed as a poor advocate for the armed forces and their needs at a time when the world can hardly be called a safe place.

The critical indicator of how far personal ambition now shapes the parliamentary Tory party is how many have “done a Fallon” – ministers, or aspirant ministers, who fervently followed David Cameron in advising of the apocalyptic results of Brexit, but who now support Theresa May (who is also, of course, a reformed Remainer). Yet, paradoxically, the trouble Daniel Hannan, an arch-Brexiteer and MEP, has had in trying to win selection to stand in Aldershot – thanks to a Central Office intervention – is said to be because the party wants no one with a “profile” on Europe to be added to the mix, in an apparent attempt to prevent adding fuel to the fire of intra-party dissent. This may appease a small hard core of pro-Remain MPs – such as Anna Soubry, who has sufficient talent to sit in the cabinet – who stick to their principles; but others are all Brexiteers now.

So if you seek an early flavour of the next Conservative administration, it is right before you: one powering on to Brexit, not only because that is what the country voted for, but because that is the orthodoxy those who wish to be ministers must devotedly follow. And though dissent will grow, few of talent wish to emulate Soubry, sitting out the years ahead as backbenchers while their intellectual and moral inferiors prosper.

Simon Heffer is a columnist for the Daily and Sunday Telegraphs

Simon Heffer is a journalist, author and political commentator, who has worked for long stretches at the Daily Telegraph and the Daily Mail. He has written biographies of Thomas Carlyle, Ralph Vaughan Williams and Enoch Powell, and reviews and writes on politics for the New Statesman

This article first appeared in the 27 April 2017 issue of the New Statesman, Cool Britannia 20 Years On

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