Here is the full text of my 22d Quartz column, “An Economist’s Mea Culpa: I Relied on Reinhart and Rogoff,” now brought home to supplysideliberal.com. The comments I made when I first flagged this column on my blog now seem outdated. You would be better advised to read my post "After Crunching Reinhart and Rogoff’s Data, We Found No Evidence that High Debt Slows Growth" and the Quartz column I wrote with Yichuan Wang that it links to. Yichuan and I plan another follow-up post to that very soon. Note that the argument below about debt raising interest rates for countries that do not have their own currency still stands, and has been amplified by Paul Andrews here, though the other worries I mention based on the Reinhart and Rogoff data set have been allayed.
I hope you notice the allusions to incentives and mechanism design below. In terms of what Carmen Reinhart and Ken Rogoff should have done that they didn’t do, “Be very careful to double-check for mistakes” is obvious. But on consideration, I also felt dismayed that they didn’t do a bit more analysis on their data early on to make a rudimentary attempt to answer the question of causality. I wouldn’t have said it quite as strongly as Matthew Yglesias, but the sentiment is basically the same.
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© April 20, 2013: Miles Kimball, as first published on Quartz. Used by permission according to a temporary nonexclusive license expiring June 30, 2014. All rights reserved.
Ken Rogoff is an economist who has always been kind to me, and for whom I have deep respect. And I have no animus toward Carmen Reinhart. Nevertheless, I hope there has been a nightmarish quality to the last few days of what Quartz writer Matt Phillips called a “bone-crunching social media pile-on that Harvard economists Ken Rogoff and Carmen Reinhart received in recent days after some other researchers questioned their influential findings that high government debt is a drag on economic growth.” I say this because I know from my own experience as a researcher how powerfully the hint of such an embarrassment motivates economists and other researchers to sweat the details to get things right. Some errors will always slip through the cracks, but a researcher ought to live in mortal fear of a contretemps like that Reinhart and Rogoff have found themselves in this week.
Reinhart and Rogoff have not only caused embarrassment for themselves, but also for all those who have in any way relied on their results. Those who made their case by overinterpreting the particular results that have now been discredited should be the most embarrassed. Quartz’s Tim Fernholz gives a rundown of politicians and other policy makers who relied heavily on Reinhart and Rogoff’s results in “How influential was the Reinhart and Rogoff study warning that high debt kills growth?”
But I, like many others, have relied on Reinhart and Rogoff’s results in smaller ways—and wish this embarrassment on myself as a warning for the future. No one is perfect, but it is important not to undercut the motivation to be careful by softening the penalty for error too much. I am lucky I can heal the damage; I have fully updated the argument I made based on Reinhart and Rogoff’s results in my column “What Paul Krugman got wrong about Italy’s economy” in a way that I think leaves the force of the overall argument in that column intact. Here in full, is the new passage, which also gives my view of the substantive issue that Reinhart and Rogoff have now occasioned so much confusion about:
And despite the recent revelation of errors in Carmen Reinhart and Ken Rogoff’s famous study of debt levels and economic growth, which I discuss here and which motivated the update you are reading (the original passage can be found here), there are reasons to think that high levels of debt are worth worrying about.
First, for a country like Italy that does not have its own currency (since it shares the euro with many other countries), Paul Krugman’s own graph shows a correlation between national debt as a percentage of GDP and the interest rate that a country pays.
Second, the paper by Thomas Herndon, Michael Ash and Robert Pollin that criticizes Reinhart and Rogoff finds that, on average, growth rates do decline with debt levels. Divide debt levels into medium high (60% to 90% of GDP), high (90% to 120% of GDP), and very high (above 120% of GDP). Then the growth rates are 3.2% with medium-high debt, 2.4% with high debt, and 1.4% with very high debt. (I got these numbers by combining the 4.2% growth rate for countries in the 0 to 30% debt-to-GDP ratio range from Table 3 with the estimates in Table 4 for how things are different at higher debt levels.) Moreover, contrary to the impression one would get from the column here, Herndon, Ash and Pollin’s Table 4 indicates that the differences between low levels of debt and high levels of debt are not just due to chance, though what Herndon, Ash and Pollin emphasize is that very low levels of debt, below 30% of GDP, have a strong association with higher growth rates. Overall, with the data we have, we don’t know what causes what, so there is no definitive answer to how much we should worry about debt, but ample reason not to treat debt as if it were a nothing. [For a more recent reassessment of that evidence, see my post "After Crunching Reinhart and Rogoff’s Data, We Found No Evidence that High Debt Slows Growth" and the Quartz column I wrote with Yichuan Wang that it links to.]
There is definitely a reasonable case to be made that if additional spending or tax cuts are the only way to stimulate the economy, then we should do it even at the cost of additional debt. But as I argue both in “What Paul Krugman got wrong about Italy’s economy” and in “Why austerity budgets won’t save your economy,” there are ways to stimulate the economy without adding to its debt burden, and stimulating the economy in a way that doesn’t add substantially to the national debt is better than stimulating the economy in a way that does.
Unlike what many politicians would do in similar circumstances, Reinhart and Rogoff have been forthright in admitting their errors. (See Chris Cook’s Financial Times post, “Reinhart and Rogoff Recrunch the Numbers.”) They also used their response to put forward their best argument that correcting the errors does not change their bottom line. Given the number of bloggers arguing the opposite case—that Reinhart and Rogoff’s bottom line has been destroyed—it is actually helpful for them to make their case in what has become an adversarial situation, despite their self-justifying motivation for doing so. And though I see a self-justifying motivation, I find it credible that Reinhart and Rogoff’s original error did not arise from political motivations, since as they note in their response, of their two major claims—(1) debt hurts growth and (2) economic slumps typically last a long time after a financial crisis—the claim that debt hurts growth is congenial to Republicans, while the claim that it is normal for slumps to last a long time after a financial crisis is congenial to Democrats. But it hurt the nation’s decision-making process when the true statement, that we should be worried high levels of national debt might have a negative effect on growth, was mangled into the idea that a debt-to-GDP ratio of 90% is a critical threshold for the effects of debt on the economy—an idea that gained the traction it did because of Reinhart and Rogoff’s mistake.