The work of Reinhart and Rogoff was a major reason for the push for austerity at a time when expansionary policy was called for, i.e. their work supported the bad idea that austerity during a recession can actually be stimulative. It isn't as the events in Europe have shown conclusively.

To be fair, as I discussed here (in "Austerity Can Wait for Sunnier Days") after watching Reinhart give a talk on this topic at an INET conference, she didn't assert that contractionary policy was somehow expansionary (i.e. she did not claim the confidence fairy would more than offset the negative short-run effects of austerity). What she asserted is that pain now -- austerity -- can avoid even more pain down the road in the form of lower economic growth.

Here's the problem. She is right that austerity causes pain in the short-run. But according to a review of her work with Rogoff discussed below, the lower growth from debt levels above 90 percent that austerity is supposed to avoid turns out, it appears, to be largely the result of errors in the research. In fact, there is no substantial growth penalty from high debt levels, and hence not much gain from short-run austerity.

Here's Dean Baker with a rundown on the new work (see also Mike Konczal who helped to shed light on this research):

How Much Unemployment Was Caused by Reinhart and Rogoff's Arithmetic Mistake?, by Dean Baker: 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. First, there is good reason for believing causation goes the other way. Countries are likely to have high debt-to-GDP ratios because they are having serious economic problems.

Second, as Josh Bivens and John Irons have pointed out, the story of the bad growth in high debt years in the United States is driven by the demobilization after World War II. In other words, these were not bad economic times, the years of high debt in the United States had slow growth because millions of women opted to leave the paid labor force.

Third, the whole notion of public debt turns out to be ill-defined. ...

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..., 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.

In fairness, there has been other research that makes similar claims, including more recent work by Reinhardt and Rogoff. But it was the initial R&R papers that created the framework for most of the subsequent policy debate. And HAP has shown that the key finding that debt slows growth was driven overwhelmingly by the exclusion of 4 years of data from New Zealand.

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.

(Those interested in playing with the data itself can find it at the website for the Political Economic Research Institute.)

Update: Reinhart-Rogoff Response to Critique - WSJ.