Free exchange
The 90% question
A seminal analysis of the relationship between debt and growth comes under attack
Apr 20th 2013 |Economist
GOVERNMENT indebtedness matters. Default and financial panic are the stuff of finance-minister nightmares. Government borrowing can crowd out private investment, dragging growth down. Yet economists have struggled to specify when a country needs to worry about its debt load. In a 2010 paper Carmen Reinhart, now a professor at Harvard Kennedy School, and Kenneth Rogoff, an economist at Harvard University, seemed to provide an answer. They argued that GDP growth slows to a snail’s pace once government-debt levels exceed 90% of GDP.
國債當然重要，問問許多財政部長就知道。無法如期償還債務和金融危機所造成的恐慌是他們目前最大的夢饜。政府舉債會排擠私人投資，拖慢經濟成長。然而經過無數的努力，經濟學家至今仍無法明確地指出一個明確的時間點─何時國家必須要擔心國債會開始拖垮國內經濟。在一份2010年發表的報告中，Carmen Reinhart(目前為哈佛甘迺迪學院教授)以及Kenneth Rogoff(哈佛大學經濟學者)似乎提供了一個答案：一旦國債超過了國民生產毛額(GDP)的90%，GDP之成長速度就會慢如牛步。
The 90% figure quickly became ammunition in political arguments over austerity. Paul Ryan, a Republican congressman, cited their “conclusive empirical evidence” in a budget plan calling for swingeing cuts to public spending. In a February letter to European Union finance ministers Olli Rehn, the vice-president of the European Commission, touted the “widely acknowledged” 90% limit as a reason to press on with European fiscal cuts. Such rhetoric has helped to make the Reinhart-Rogoff number the subject of bitter dispute. And this week a new piece of research poured fuel on the fire by calling the 90% finding into question.
90%這個數字迅速地成為了政府為其撙節政策辯護的重要依據。共和黨國會議員Paul Ryan在其預算計畫書中便引述Reinhart和 Rogoff此一從「觀察得來的實證」，要求大幅刪砍公共支出。另外，歐委會副總理Olli Regn在2月時寫了封信給歐盟國各財政部長，兜售90%上限這個「公認」的概念，並認為這就是為什麼歐洲各國需加緊削減其財務支出。這一系列的論述讓Reinhart和Rogoff兩人成為許多激烈爭論的主角。而於本周新發表的一篇研究則根本上質疑90%的正確性，讓爭論愈演愈烈。
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.
兩名教授在2010年採用的計算程式並不算太難。在其2009年的一篇名為「這一次有所不同的」的金融史報告中，他們引用了逾兩世紀的數據(此篇報告的研究結果成為日後90%門檻的基礎)，然後將蒐集到的數據分成四種不同的負債類型，並計算出每一種類型的平均成長率。
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.
他們發現若國債未超過GDP的90%，則對經濟成長將不會有太大的影響。不過一旦超過此臨界點，則成長率將大幅下滑。整整兩個世紀的數據顯示，一旦國債超過了90%大關，平均成長率將從3%降到僅剩1.7%。在大戰結束後的短期內，衰退幅度更是劇烈，若是國債達到90%，平均成長率甚至會出現負成長(從3%直接下滑到-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.
此與以往完全不同的明確論述引起了廣泛的關注。用經濟學的行話來說，債務和成長之間的關係並不是「線性」─當債務上升時成長率就會隨之一步步下滑。相反地，直至臨界點前，債務看起來都還是良性的，但一旦超過臨界點，國債就會對整體經濟產生不良影響。兩名作者認為一旦國債超過90%的門檻，市場對風險的認知就會大大提升，這將可能導致急遽上升的利息或造成金融市場的壓力，迫使政府須做出艱難抉擇: 撙節、通膨或是拖延還款期限。
文章定位：
