作者：Robert J. Samuelson 2012年3月7日 The Washington Post

Does China already have the world’s largest economy? Most economists think not, and there’s a widespread guessing game as to when it will. “Sometime in the next decade” is a common answer, depending on how fast the United States — today’s No. 1 — and China grow. But some economists believe the crossover has already occurred. If so, this would be an event of huge symbolic importance, conferring at least bragging rights to China. But is it so?

In a recent blog post, Arvind Subramanian of the Peterson Institute for International Economics argues that China passed the United States in 2010 or earlier. He says the World Bank and International Monetary Fund, which publish widely used estimates of nations’ output (gross domestic product), have vastly understated China’s economy.

Let’s look at the numbers. In 2010, according to the World Bank figures, China’s economy was about 70 percent the size of America’s. Its GDP totaled $10.2 trillion, compared with U.S. GDP of $14.6 trillion. The trouble, contends Subramanian, is that the United States’s lead is a statistical illusion and that China’s GDP is about 47 percent larger than the official estimates. This would bring the 2010 figure to $15 trillion, slightly ahead of the U.S. GDP. Indeed, says Subramanian, a new study suggests the underestimate could be more than 70 percent. This implies China’s 2010 GDP exceeded $17 trillion.

What are we to make of this?

For starters, keep matters in perspective. Living standards in the United States, as measured by per capita incomes, remain much higher than in China under any of the GDP estimates. Remember that all of China’s production and income are spread over 1.34 billion people while U.S. GDP is divided among 309 million Americans. Using the official World Bank figures, U.S. per capita income totaled $47,153 in 2010, compared with China’s $7,599. Assuming a Chinese GDP of $17 trillion raises per capita income to about $12,700; that’s roughly a fourth of the U.S. level.

Next, understand that the dispute is deeply technical. There are two uncertainties: first, the reliability of Chinese production and price data used to estimate GDP in renminbi (RMB); and second, the conversion of the RMB figures into dollars to permit international comparisons. This second stage, called “purchasing power parity” (PPP), involves finding a common way to measure output in different countries.

To simplify slightly: If an item costs 6 RMB in China and $1 in the United States, the Chinese item would be assigned a value of $1. The problem is that although many items are similar among advanced countries — a Toyota is a Toyota — big differences exist between rich and poor nations. Ways have to be found to measure items that aren’t common everywhere.

This task falls to the World Bank. It supervises the International Comparison Program (ICP) that collects statistics and applies PPP methods to 197 countries and economies. This process establishes an overall relation between local prices in each country and dollar prices in the United States. But the integrity of the results depends upon the accuracy of the local prices. A major complaint about China’s GDP figures is that the surveys underrepresented rural areas, where prices are lower. World Bank economists say any distortion is modest; but Subramanian and others see it as a big source of underestimation.

The issue may not be settled conclusively until the end of 2013; that’s when the latest revision of the ICP, creating new “benchmark” statistics, is scheduled for completion. Meanwhile, it’s interesting to estimate when China might overtake the United States in GDP if today’s official estimates are correct. Assuming China grows 8 percent annually and the United States 3 percent — both assumptions may be a bit on the high side — the crossover would occur in 2018.

塞缪尔森：中国或将于2018年超过美国

中国已成为世界头号经济体了吗？大多数经济学家不这样认为，关于它何时成为世界头号经济体存在着广泛的猜测。一种普遍的看法是"在未来十年的某个时间"，这还取决于目前世界头号经济体美国与中国增速的快慢。假如真是这样，这将是一件具有重大象征意义的事，至少将赋予中国夸耀的权力。然而，事实果真如此吗？

　　彼得森国际经济研究所阿尔温德·苏布拉马尼安在最近发表的博客文章中认为，中国在2010年或更早的时候就已超越美国成为世界头号经济体。他说世界银行和国际货币基金组织大大低估了中国的经济。世界银行和国际货币基金组织负责公布被广泛采用的各国产值（国内生产总值）的评估值。

让我们来看一下这些数字。世界银行的统计数字显示，2010年中国的经济总量是美国的70%。中国GDP的总额为10.2万亿美元，而美国的GDP为14.6万亿美元。苏布拉马尼安认为问题在于美国的领先是统计数据上的假象，中国的GDP比官方估计的数值要高约47%。这会使得中国2010年GDP数值达到15万亿美元，稍稍领先于美国的GDP。苏布拉马尼安说，最新的一项研究认为对中国GDP的低估超过了70%。这意味着中国2010年的GDP就已超过了17万亿美元。

　　我们如何解释这一现象？

　　首先，应全面地看待问题。不论在何种GDP的估算下，按人均收入衡量，美国的生活水平比中国要高很多。别忘了中国的总产值和总收入是需要分配到13.4亿人身上，而美国的GDP则是分给3.09亿人。世界银行的官方数据显示，2010年美国的人均收入为4.7153万美元，相比之下，中国为7599美元。假设中国的GDP为17万亿美元，这将使中国的人均收入达到1.27万美元，大约是美国的四分之一。

　　其次，应明白这种争论是技术层面上的。存在两种不确定的因素：第一，用于估算中国产值和价格数据的可信度；其二，人民币兑换成美元产生的结果。第二点不确定因素被称为"购买力平价"，是一种衡量不同国家产值的常用方法。

　　简而言之：如果一件产品在中国的价格为6元人民币，在美国为1美元，那么这件中国产品的价值可以被估算为1美元。问题是在发达国家很多产品都类似（丰田就是丰田），但在富国和穷国之间存在很大差距。必须找到衡量不是在各国都共同存在的产品价值的方法。

　　这个任务落到了世界银行身上。它负责监督国际可比项目（ICP），该项目旨在收集数据，并向197个国家和经济体提供购买力平价评估。这一评估方法在各国的本国价格与美国的美元价格之间建立起联系。不过，评估结果的公正取决于本国价格的准确性。对中国GDP数值的主要抱怨在于调查结果低估了农村地区，其产品价值相对较低。世界银行的经济学家说数据偏差是适度的，但苏布拉马尼安和其他专家认为农村是产品价值被低估的主要地区。

　　国际可比项目将于2013年年底完成最新修订，制订出新的"基准"数据。就到那时，这一问题最后也不可能得到解决。此外，假设目前官方评估数据是准确的，那么预测中国可能何时超过美国会有点意思。假定中国的年增长率为8%，美国为3%（两种假设可能都有些偏高），那么中国超过美国的交叉点将会出现在2018年。