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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Debunking Boris Johnson's claim that energy bills will be lower if we leave the EU

Why the Brexiteers' energy policy is less power to the people and more electric shock.

Boris Johnson and Michael Gove have promised that they will end VAT on domestic energy bills if the country votes to leave in the EU referendum. This would save Britain £2bn, or "over £60" per household, they claimed in The Sun this morning.

They are right that this is not something that could be done without leaving the Union. But is such a promise responsible? Might Brexit in fact cost us much more in increased energy bills than an end to VAT could ever hope to save? Quite probably.

Let’s do the maths...

In 2014, the latest year for which figures are available, the UK imported 46 per cent of our total energy supply. Over 20 other countries helped us keep our lights on, from Russian coal to Norwegian gas. And according to Energy Secretary Amber Rudd, this trend is only set to continue (regardless of the potential for domestic fracking), thanks to our declining reserves of North Sea gas and oil.


Click to enlarge.

The reliance on imports makes the UK highly vulnerable to fluctuations in the value of the pound: the lower its value, the more we have to pay for anything we import. This is a situation that could spell disaster in the case of a Brexit, with the Treasury estimating that a vote to leave could cause the pound to fall by 12 per cent.

So what does this mean for our energy bills? According to December’s figures from the Office of National Statistics, the average UK household spends £25.80 a week on gas, electricity and other fuels, which adds up to £35.7bn a year across the UK. And if roughly 45 per cent (£16.4bn) of that amount is based on imports, then a devaluation of the pound could cause their cost to rise 12 per cent – to £18.4bn.

This would represent a 5.6 per cent increase in our total spending on domestic energy, bringing the annual cost up to £37.7bn, and resulting in a £75 a year rise per average household. That’s £11 more than the Brexiteers have promised removing VAT would reduce bills by. 

This is a rough estimate – and adjustments would have to be made to account for the varying exchange rates of the countries we trade with, as well as the proportion of the energy imports that are allocated to domestic use – but it makes a start at holding Johnson and Gove’s latest figures to account.

Here are five other ways in which leaving the EU could risk soaring energy prices:

We would have less control over EU energy policy

A new report from Chatham House argues that the deeply integrated nature of the UK’s energy system means that we couldn’t simply switch-off the  relationship with the EU. “It would be neither possible nor desirable to ‘unplug’ the UK from Europe’s energy networks,” they argue. “A degree of continued adherence to EU market, environmental and governance rules would be inevitable.”

Exclusion from Europe’s Internal Energy Market could have a long-term negative impact

Secretary of State for Energy and Climate Change Amber Rudd said that a Brexit was likely to produce an “electric shock” for UK energy customers – with costs spiralling upwards “by at least half a billion pounds a year”. This claim was based on Vivid Economic’s report for the National Grid, which warned that if Britain was excluded from the IEM, the potential impact “could be up to £500m per year by the early 2020s”.

Brexit could make our energy supply less secure

Rudd has also stressed  the risks to energy security that a vote to Leave could entail. In a speech made last Thursday, she pointed her finger particularly in the direction of Vladamir Putin and his ability to bloc gas supplies to the UK: “As a bloc of 500 million people we have the power to force Putin’s hand. We can coordinate our response to a crisis.”

It could also choke investment into British energy infrastructure

£45bn was invested in Britain’s energy system from elsewhere in the EU in 2014. But the German industrial conglomerate Siemens, who makes hundreds of the turbines used the UK’s offshore windfarms, has warned that Brexit “could make the UK a less attractive place to do business”.

Petrol costs would also rise

The AA has warned that leaving the EU could cause petrol prices to rise by as much 19p a litre. That’s an extra £10 every time you fill up the family car. More cautious estimates, such as that from the RAC, still see pump prices rising by £2 per tank.

The EU is an invaluable ally in the fight against Climate Change

At a speech at a solar farm in Lincolnshire last Friday, Jeremy Corbyn argued that the need for co-orinated energy policy is now greater than ever “Climate change is one of the greatest fights of our generation and, at a time when the Government has scrapped funding for green projects, it is vital that we remain in the EU so we can keep accessing valuable funding streams to protect our environment.”

Corbyn’s statement builds upon those made by Green Party MEP, Keith Taylor, whose consultations with research groups have stressed the importance of maintaining the EU’s energy efficiency directive: “Outside the EU, the government’s zeal for deregulation will put a kibosh on the progress made on energy efficiency in Britain.”

India Bourke is the New Statesman's editorial assistant.