Tweet..THIS week's Free exchange column discusses the week's hot macroeconomic controversy:
本周的自由交流栏目讨论了热点宏观经济的争论。

In a 2010 paper* Carmen Reinhart, now a professor at Harvard Kennedy School, and Kenneth Rogoff, an economist at Harvard University...argued that GDP growth slows to a snail’s pace once government-debt levels exceed 90% of GDP. The 90% figure quickly became ammunition in political arguments over austerity...[T]his week a new piece of research poured fuel on the fire by calling the 90% finding into question.
2010年，现任哈佛大学肯尼迪政府学院教授卡门·莱因哈特与哈佛大学经济学家肯尼思·罗格夫认为，国内生产总值GDP增长放缓，政府债务水平超过了GDP的90%，90%这个数字很快成为了政治争论关于紧缩的弹丸热点。星期一他的一份新的研究更加推波助澜，通过调用90%这个数字深入探究问题。
   
The 2010 calculation was a relatively simple one. The authors had already drawn on two centuries of public-debt data for their seminal 2009 financial history, “This Time is Different”. In their paper Ms Reinhart and Mr Rogoff sorted the figures into four categories of indebtedness and took average growth rates for each. They found that public debt has little effect on growth rates until debt reaches 90% of GDP. Growth rates then drop sharply. Over the entire two-century sample (from 1790 to 2009), average growth sinks from more than 3% a year to just 1.7% once debt rises above the critical level. In a shorter post-war sample the decline is more dramatic; average growth drops from around 3% to -0.1% after the 90%-of-GDP threshold is attained.
2012年的计算是一个相对简单的数字。作者已经画出了2009年金融历史开创性的两个世纪公共债务。这一次是不同的。莱因哈特和罗格夫先生在研究论文中把债务按照数字排序分成四类，并为每个计算出平均增长率。他们发现，公共债务对增长率的影响不大，一直到债务达到GDP的90%的时候，增长率急剧下降。整个两个世纪的抽样（从1790年到2009年），在平均增长率大于3%的年份中仅有1.7%的债务增长超过了临界值。之后的下降更具有戏剧性，在政府债务水平超过了GDP的90%后，平均增长从3%下降到负0.1%。

The sharpness of this turning-point excited lots of attention. In economic jargon the debt-growth relationship was not “linear”, with growth rates gliding steadily downward as borrowing rises. Instead, debt levels look benign until a critical point is reached, and then they don’t. The authors reckoned that beyond the 90% threshold, market perceptions of risk can jump. That could translate into soaring interest rates or financial-market stress, forcing hard choices: austerity, inflation or default.
这个清晰的转折点引起了许多关注。用经济术语来说，债务增长的相关性不是呈现线性的，随着借贷上升增长率稳步下降，相反，债务水平保持温和，一直到达到了临界点后就不是如此变化了。作者认为超过90%是一个门槛，市场的风险可是跳跃性的。这会转化为飙升的利率或金融市场的压力，迫使艰难的选择：财政紧缩、通货膨胀、或者默认。

The new paper, by Thomas Herndon, Michael Ash and Robert Pollin of the University of Massachusetts, Amherst, sought to replicate the Reinhart-Rogoff result for the post-war period. They reckon that mistakes in the analysis led Ms Reinhart and Mr Rogoff to understate average growth at high debt levels...Taken together, the authors of the new paper reckon that average post-war growth above the 90% threshold ought to have been reported at 2.2% rather than -0.1% (see chart).
麻萨诸塞大学安模斯特分校经济学家赫恩敦(Thomas Herndon)、艾希(Michael Ash)和波伦(Robert Pollin)的战后时期研究显示，他们认为在分析中误导了莱因哈特和罗格夫低估了高债务水平时的平均增长，总之，研究报告的作者认为，公债超过GDP90%的国家，战后平均增长率是2.2%，而不是如莱因哈特和罗格夫文章中所说的负0.1%。

The new paper set tongues wagging in Washington, DC, where policymakers gathered this week for the annual spring meetings of the IMF and the World Bank. Yet there is less dissonance between the two studies than you might imagine. In a response to the Herndon-Ash-Pollin paper, Ms Reinhart and Mr Rogoff acknowledge the coding error. They also ascribe apparently “missing” data to the fact that their data set is a work in progress. Updates of their analysis, published later in 2010 and in 2012, incorporate newly added figures, for example.
本周国际货币基金组织IMF和世界银行年度春季会议在华盛顿特区召开，新的研究令齐聚的决策者们伸伸舌头。然而，两个研究之间很少不一致，比你想象的还少。赫恩顿、艾希、波伦回应说，莱因哈特和罗格夫承认了有编码错误，他们认为很明显有丢失的数据。事实上，他们的数据收集是一个进展中的研究。他们的分析会不断更新，例如，在2012和2012年后的研究结果发布将会有新增的数据。


More importantly, Ms Reinhart and Mr Rogoff point out that they did not stress any single number in their analysis, but consistently used several calculations. They computed the average over both the post-war period and the two-century time span. They also presented “median” growth rates across thresholds, as well as mean rates. In their 2010 paper, the median growth rate above the 90% threshold is 1.9% during the 1790-2009 period and 1.6% in the post-war period. Those results are in the same ballpark as the Herndon-Ash-Pollin figure, argue Ms Reinhart and Mr Rogoff.
更重要的是，莱因哈特女士和罗格夫先生指出他们的分析中不强调任何一个单一数字，一贯使用几种计算方法。计算了战后两个时期平均数字。他们提出了“中位数”的增长率还有平均率。在2010年的论文中，达到了90%临界点以上平均增长率是1.9%而在1790年至2009年战后增长率是1.6%。莱因哈特女士和罗格夫先生的这个研究结果与赫恩顿、艾希、波伦的研究数字是一样的。

来源：经济学人
Apr 17th 2013, 20:53 by R.A. | WASHINGTON
作者：R.A（华盛顿）
时间：2013年4月17日
翻译：龚蕾
原文地址：http://www.economist.com/blogs/freeexchange/2013/04/debt-and-growth