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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Labour's establishment suspects a Momentum conspiracy - they're right

Bernie Sanders-style organisers are determined to rewire the party's machine.  

If you wanted to understand the basic dynamics of this year’s Labour leadership contest, Brighton and Hove District Labour Party is a good microcosm. On Saturday 9 July, a day before Angela Eagle was to announce her leadership bid, hundreds of members flooded into its AGM. Despite the room having a capacity of over 250, the meeting had to be held in three batches, with members forming an orderly queue. The result of the massive turnout was clear in political terms – pro-Corbyn candidates won every position on the local executive committee. 

Many in the room hailed the turnout and the result. But others claimed that some in the crowd had engaged in abuse and harassment.The national party decided that, rather than first investigate individuals, it would suspend Brighton and Hove. Add this to the national ban on local meetings and events during the leadership election, and it is easy to see why Labour seems to have an uneasy relationship with mass politics. To put it a less neutral way, the party machine is in a state of open warfare against Corbyn and his supporters.

Brighton and Hove illustrates how local activists have continued to organise – in an even more innovative and effective way than before. On Thursday 21 July, the week following the CLP’s suspension, the local Momentum group organised a mass meeting. More than 200 people showed up, with the mood defiant and pumped up.  Rather than listen to speeches, the room then became a road test for a new "campaign meetup", a more modestly titled version of the "barnstorms" used by the Bernie Sanders campaign. Activists broke up into small groups to discuss the strategy of the campaign and then even smaller groups to organise action on a very local level. By the end of the night, 20 phonebanking sessions had been planned at a branch level over the following week. 

In the past, organising inside the Labour Party was seen as a slightly cloak and dagger affair. When the Labour Party bureaucracy expelled leftwing activists in past decades, many on went further underground, organising in semi-secrecy. Now, Momentum is doing the exact opposite. 

The emphasis of the Corbyn campaign is on making its strategy, volunteer hubs and events listings as open and accessible as possible. Interactive maps will allow local activists to advertise hundreds of events, and then contact people in their area. When they gather to phonebank in they will be using a custom-built web app which will enable tens of thousands of callers to ring hundreds of thousands of numbers, from wherever they are.

As Momentum has learned to its cost, there is a trade-off between a campaign’s openness and its ability to stage manage events. But in the new politics of the Labour party, in which both the numbers of interested people and the capacity to connect with them directly are increasing exponentially, there is simply no contest. In order to win the next general election, Labour will have to master these tactics on a much bigger scale. The leadership election is the road test. 

Even many moderates seem to accept that the days of simply triangulating towards the centre and getting cozy with the Murdoch press are over. Labour needs to reach people and communities directly with an ambitious digital strategy and an army of self-organising activists. It is this kind of mass politics that delivered a "no" vote in Greece’s referendum on the terms of the Eurozone bailout last summer – defying pretty much the whole of the media, business and political establishment. 

The problem for Corbyn's challenger, Owen Smith, is that many of his backers have an open problem with this type of mass politics. Rather than investigate allegations of abuse, they have supported the suspension of CLPs. Rather than seeing the heightened emotions that come with mass mobilisations as side-effects which needs to be controlled, they have sought to joins unconnected acts of harassment, in order to smear Jeremy Corbyn. The MP Ben Bradshaw has even seemed to accuse Momentum of organising a conspiracy to physically attack Labour MPs.

The real conspiracy is much bigger than that. Hundreds of thousands of people are arriving, enthusiastic and determined, into the Labour party. These people, and their ability to convince the communities of which they are a part, threaten Britain’s political equilibrium, both the Conservatives and the Labour establishment. When the greatest hope for Labour becomes your greatest nightmare, you have good call to feel alarmed.