The Excel error that ruined the world

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The Excel error that ruined the world

via Hullabaloo by (digby) on 4/16/13

The Excel error that ruined the world

by digby

I have to admit I never expected that among the reasons the elites have been pursuing a daft economic policy over the past few years was a simple calculation error. Here’s Dean Baker:

How Much Unemployment Was Caused by Reinhart and Rogoff’s Arithmetic Mistake?

That’s the question millions will be asking when they see the new paper by my friends at the University of Massachusetts, Thomas Herndon, Michael Ash, and Robert Pollin. Herndon, Ash, and Pollin (HAP) corrected the spreadsheets of Carmen Reinhart and Ken Rogoff. They show the correct numbers tell a very different story about the relationship between debt and GDP growth than the one that Reinhart and Rogoff have been hawking.

Just to remind folks, Reinhart and Rogoff (R&R) are the authors of the widely acclaimed book on the history of financial crises, This Time is Different. They have also done several papers derived from this research, the main conclusion of which is that high ratios of debt to GDP lead to a long periods of slow growth. Their story line is that 90 percent is a cutoff line, with countries with debt-to-GDP ratios above this level seeing markedly slower growth than countries that have debt-to-GDP ratios below this level. The moral is to make sure the debt-to-GDP ratio does not get above 90 percent.

There are all sorts of good reasons for questioning this logic.


But HAP tells us that we need not concern ourselves with any arguments this complicated. The basic R&R story was simply the result of them getting their own numbers wrong.

After being unable to reproduce R&R’s results with publicly available data, HAP were able to get the spreadsheets that R&R had used for their calculations. It turns out that the initial results were driven by simple computational and transcription errors. The most important of these errors was excluding four years of growth data from New Zealand in which it was above the 90 percent debt-to-GDP threshold. When these four years are added in, the average growth rate in New Zealand for its high debt years was 2.6 percent, compared to the -7.6 percent that R&R had entered in their calculation.

Since R&R country weight their data (each country’s growth rate has the same weight), and there are only seven countries that cross into the high debt region, correcting this one mistake alone adds 1.5 percentage points to the average growth rate for the high debt countries. This eliminates most of the falloff in growth that R&R find from high debt levels. (HAP find several other important errors in the R&R paper, however the missing New Zealand years are the biggest part of the story.)

This is a big deal because politicians around the world have used this finding from R&R to justify austerity measures that have slowed growth and raised unemployment. In the United States many politicians have pointed to R&R’s work as justification for deficit reduction even though the economy is far below full employment by any reasonable measure. In Europe, R&R’s work and its derivatives have been used to justify austerity policies that have pushed the unemployment rate over 10 percent for the euro zone as a whole and above 20 percent in Greece and Spain. In other words, this is a mistake that has had enormous consequences.
If facts mattered in economic policy debates, this should be the cause for a major reassessment of the deficit reduction policies being pursued in the United States and elsewhere. It should also cause reporters to be a bit slower to accept such sweeping claims at face value.

This doesn’t excuse the politicians around the world completely ignoring all the real world evidence showing that their policies are making things worse everywhere. This study just very conveniently gave them all reason to pursue the policies they already wanted to pursue. But the model on which they depended to sell their preferred policies has been discredited and now it’s up to them to explain why they are still intent upon pursuing them.

We can start with the United States congress, particularly Paul Ryan, and the White House.

Update: Mike Konzcal has much more, but this really takes the cake:

Coding Error.

As Herndon-Ash-Pollin puts it: “A coding error in the RR working spreadsheet entirely excludes five countries, Australia, Austria, Belgium, Canada, and Denmark, from the analysis. [Reinhart-Rogoff] averaged cells in lines 30 to 44 instead of lines 30 to 49…This spreadsheet error…is responsible for a -0.3 percentage-point error in RR’s published average real GDP growth in the highest public debt/GDP category.” Belgium, in particular, has 26 years with debt-to-GDP above 90 percent, with an average growth rate of 2.6 percent (though this is only counted as one total point due to the weighting above).

Being a bit of a doubting Thomas on this coding error, I wouldn’t believe unless I touched the digital Excel wound myself. One of the authors was able to show me that, and here it is. You can see the Excel blue-box for formulas missing some data.

This error is needed to get the results they published, and it would go a long way to explaining why it has been impossible for others to replicate these results. If this error turns out to be an actual mistake Reinhart-Rogoff made, well, all I can hope is that future historians note that one of the core empirical points providing the intellectual foundation for the global move to austerity in the early 2010s was based on someone accidentally not updating a row formula in Excel.

I wouldn’t let the politicians off so easy — they were looking for this “evidence” and were lucky that it was provided for them. It’s not as if they haven’t had ample other evidence proving their policies are counter-productive. They chose what to believe.


Things you can do from here:


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