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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Why isn't Labour putting forward Corbynite candidates?

Despite his successes as a candidate, the organisational victories have gone the way of Corbyn's opponents. 

The contest changes, but the result remains the same: Jeremy Corbyn’s preferred candidate defeated in a parliamentary selection. Afzhal Khan is Labour’s candidate in the Manchester Gorton by-election and the overwhelming favourite to be the seat’s next MP.

Although Khan, an MEP, was one of  the minority of Labour’s European MPs to dissent from a letter from the European parliamentary Labour party calling for Jeremy Corbyn to go in the summer of 2016, he backed Andy Burnham and Tom Watson in 2015, and it is widely believed, fairly or unfairly, that Khan had, as one local activist put it, “the brains to know which way the wind was blowing” rather than being a pukka Corbynite.

For the leader’s office, it was a double defeat;  their preferred candidate, Sam Wheeler, was kept off the longlist, when the party’s Corbynsceptics allied with the party’s BAME leadership to draw up an all ethnic minority shortlist, and Yasmine Dar, their back-up option, was narrowly defeated by Khan among members in Manchester Gorton.

But even when the leadership has got its preferred candidate to the contest, they have been defeated. That even happened in Copeland, where the shortlist was drawn up by Corbynites and designed to advantage Rachel Holliday, the leader’s office preferred candidate.

Why does the Labour left keep losing? Supporters combination of bad luck and bad decisions for the defeat.

In Oldham West, where Michael Meacher, a committed supporter of Jeremy Corbyn’s, was succeeded by Jim McMahon, who voted for Liz Kendall, McMahon was seen to be so far ahead that they had no credible chance of stopping him. Rosena Allin-Khan was a near-perfect candidate to hold the seat of Tooting: a doctor at the local hospital, the seat’s largest employer, with links to both the Polish and Pakistani communities that make up the seat’s biggest minority blocs.  Gillian Troughton, who won the Copeland selection, is a respected local councillor.

But the leadership has also made bad decisions, some claim.  The failure to get a candidate in Manchester Gorton was particularly egregious, as one trade unionist puts it: “We all knew that Gerald was not going to make it [until 2020], they had a local boy with good connections to the trade unions, that contest should have been theirs for the taking”. Instead, they lost control of the selection panel because Jeremy Corbyn missed an NEC meeting – the NEC is hung at present as the Corbynsceptics sacrificed their majority of one to retain the chair – and with it their best chance of taking the seat.

Others close to the leadership point out that for the first year of Corbyn’s leadership, the leader’s office was more preoccupied with the struggle for survival than it was with getting more of its people in. Decisions in by-elections were taken on the hop and often in a way that led to problems later down the line. It made sense to keep Mo Azam, from the party’s left, off the shortlist in Oldham West when Labour MPs were worried for their own seats and about the Ukip effect if Labour selected a minority candidate. But that enraged the party’s minority politicians and led directly to the all-ethnic-minority shortlist in Manchester Gorton.

They also point out that the party's councillor base, from where many candidates are drawn, is still largely Corbynsceptic, though they hope that this will change in the next round of local government selections. (Councillors must go through a reselection process at every election.)

But the biggest shift has very little to do with the Labour leadership. The big victories for the Labour left in internal battles under Ed Miliband were the result of Unite and the GMB working together. Now they are, for various reasons, at odds and the GMB has proven significantly better at working shortlists and campaigning for its members to become MPs.  That helps Corbynsceptics. “The reason why so many of the unions supported Jeremy the first time,” one senior Corbynite argues, “Is they wanted to move the Labour party a little bit to the left. They didn’t want a socialist transformation of the Labour party. And actually if you look at the people getting selected they are not Corbynites, but they are not Blairites either, and that’s what the unions wanted.”

Regardless of why, it means that, two years into Corbyn’s leadership, the Labour left finds itself smaller in parliament than it was at the beginning.  

Stephen Bush is special correspondent at the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to British politics.