I’ve been a bit mystified by Excel-gate (see this good, balanced summary by Gavyn Davies). Bravo for Thomas Herndon, the graduate student who uncovered the error in the now-notorious paper by Carmen Reinhardt and Kenneth Rogoff; his job prospects will be rightly enhanced by this episode.

But the glee with which anti-Austerians pounced on this episode to ‘prove’ that austerity doesn’t work seems to involve an assumption that the original Reinhardt-Rogoff paper of 2010 ‘proved’ anything to the contrary in the first place. There are lots of papers about the impact of debt/GDP ratios on growth, and they demonstrate all kinds of different things – see for example this BIS paper by Cecchetti and others, or this IMF paper (pdf) from last year on the Caribbean economies, or this Fed paper published in December (pdf), or this much-cited 2010 paper by Koehler-Geib and others, or for that matter the new paper debunking Reinhardt and Rogoff’s 90% as it too finds the same correlation albeit with different numbers.

Well, you get the idea. Taking these together, we ‘know’ there might be a threshold for sovereign debt, but it varies over time and across countries, it’s a correlation whose causal direction and mechanism is unclear, and there isn’t enough data for any estimates to be robust (because history only runs once). All of which only goes to underline how little is known about the macroeconomy, not to mention how hard any macroeconomists and their camp followers find it to resist claiming certainty where there is none.

No doubt Reinhardt and Rogoff were tempted into over-claiming for their work by the politicisation of the debt threshold issue. But the underlying message of their big 2009 book, [amazon_link id=”0691152640″ target=”_blank” ]This Time is Different[/amazon_link], is unscathed: unlike the later paper, it makes it absolutely clear that debt ‘thresholds’ above which increasing borrowing is correlated with lower growth vary widely in different countries and at different times (no magic 90% here); and that the historical record indicates it generally takes a long time for growth to recover after banking crises involving debt overhangs.

[amazon_image id=”0691152640″ link=”true” target=”_blank” size=”medium” ]This Time Is Different: Eight Centuries of Financial Folly[/amazon_image]