Carmen Reinhart and Ken Rogoff have had a bad day. The two economic historians’ research, which implied that public debt overhangs can hamper economic growth, was perhaps one of the most cited pieces of work in recent years. Their advice that high debt-GDP ratios – particularly above 90 per cent – are harmful to growth, has become a widely used point in discussion. And it’s under attack by a trio at the University of Massachusetts, Amherst – Thomas Herndon, Michael Ash, and Robert Pollin.
As FT Alphaville has noted, the issue is about one of Reinhart and Rogoff’s most heavily cited papers on the importance of debt. This paper has been accused of being the victim of fat-fingered Excel coding, as well as selective use of data and odd weighting of how different episodes are weighted, which seemed – to the authors – to make little sense.
Robin Harding posted Reinhart and Rogoff’s original reply here. Overnight, the authors have worked through the numbers – and have put up a pretty robust defence of their work. They do admit the first error – there was an Excel blunder:
…Herndon, Ash and Pollin accurately point out the coding error that omits several countries from the averages in figure 2. Full stop. HAP are on point. The authors show our accidental omission has a fairly marginal effect on the 0-90% buckets in figure 2. However, it leads to a notable change in the average growth rate for the over 90% debt group.
They are, however, resisting the second issue – the selective use of data.
HAP go on to note some other missing debt data points, which they describe as “selective omissions”. 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.