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.

Photo:Getty
Show Hide image

Labour is a pioneer in fighting sexism. That doesn't mean there's no sexism in Labour

While we campaign against misogyny, we must not fall into the trap of thinking Labour is above it; doing so lets women members down and puts the party in danger of not taking them seriously when they report incidents. 

I’m in the Labour party to fight for equality. I cheered when Labour announced that one of its three Budget tests was ensuring the burden of cuts didn’t fall on women. I celebrated the party’s record of winning rights for women on International Women’s Day. And I marched with Labour women to end male violence against women and girls.

I’m proud of the work we’re doing for women across the country. But, as the Labour party fights for me to feel safer in society, I still feel unsafe in the Labour party.

These problems are not unique to the Labour party; misogyny is everywhere in politics. You just have to look on Twitter to see women MPs – and any woman who speaks out – receiving rape and death threats. Women at political events are subject to threatening behaviour and sexual harassment. Sexism and violence against women at its heart is about power and control. And, as we all know, nowhere is power more highly-prized and sought-after than in politics.

While we campaign against misogyny, we must not fall into the trap of thinking Labour is above it; doing so lets women members down and puts the party in danger of not taking them seriously when they report incidents. 

The House of Commons’ women and equalities committee recently stated that political parties should have robust procedures in place to prevent intimidation, bullying or sexual harassment. The committee looked at this thanks to the work of Gavin Shuker, who has helped in taking up this issue since we first started highlighting it. Labour should follow this advice, put its values into action and change its structures and culture if we are to make our party safe for women.

We need thorough and enforced codes of conduct: online, offline and at all levels of the party, from branches to the parliamentary Labour party. These should be made clear to everyone upon joining, include reminders at the start of meetings and be up in every campaign office in the country.

Too many members – particularly new and young members – say they don’t know how to report incidents or what will happen if they do. This information should be given to all members, made easily available on the website and circulated to all local parties.

Too many people – including MPs and local party leaders – still say they wouldn’t know what to do if a local member told them they had been sexually harassed. All staff members and people in positions of responsibility should be given training, so they can support members and feel comfortable responding to issues.

Having a third party organisation or individual to deal with complaints of this nature would be a huge help too. Their contact details should be easy to find on the website. This organisation should, crucially, be independent of influence from elsewhere in the party. This would allow them to perform their role without political pressures or bias. We need a system that gives members confidence that they will be treated fairly, not one where members are worried about reporting incidents because the man in question holds power, has certain political allies or is a friend or colleague of the person you are supposed to complain to.

Giving this third party the resources and access they need to identify issues within our party and recommend further changes to the NEC would help to begin a continuous process of improving both our structures and culture.

Labour should champion a more open culture, where people feel able to report incidents and don't have to worry about ruining their career or facing political repercussions if they do so. Problems should not be brushed under the carpet. It takes bravery to admit your faults. But, until these problems are faced head-on, they will not go away.

Being the party of equality does not mean Labour is immune to misogyny and sexual harassment, but it does mean it should lead the way on tackling it.

Now is the time for Labour to practice what it preaches and prove it is serious about women’s equality.

Bex Bailey was on Labour’s national executive committee from 2014 to 2016.