如果中国经济年增长率仅为2%，那将是怎样的情形？鉴于中国在过去30年的表现，这听起来像是一个悲观到荒谬程度的问题。当然，中国存在多方面的问题。事实上，中国经济已开始放缓。但是，什么样的灾难才可能把中国增速拉到如此惨不忍睹的地步呢？
根据美国经济学家兰特•普里切特(Lant Pritchett)和劳伦斯•萨默斯(Lawrence Summers)的一份颇有影响力的论文，这是一个错误的问题。在他们看来，有关增长的“唯一最强大和惊人的事实”是“回归（约2%的）均值”。他们说，在现代历史上，只在极少的情况下，国家才能将超过6%的“超高速”增长维持10年以上。而自1977年以来，中国通过调动市场力量突破了这个惯常趋势，缔造了“人类历史上”可能最长的高速增长期。但这两位作者告诉我们，有升必有降。
他们在梳理数据之后，得出两条强大的结论。其一是，通过一个十年预测下一个十年的增长，几乎没有统计学基础。外推法是一种傻瓜游戏——或者如他们所言，“目前的增长对预测未来几乎毫无作用”。从1967年到1980年，巴西的年均增长率为5.2%。当时很少有人会预测，在接下来22年巴西人均收入增长率将恰好为零。
他们的第二项发现是，超高速增长期的平均长度是9年。中国大陆是一个很大的例外。唯有台湾和韩国的表现与其接近，它们的高速增长期分别为32年和29年。两位作者表示，一旦这样的增长期结束，增长率降幅的均值是4.65个百分点。按此计算，中国的经济增长率将降至4%，印度将降至1.6%——远低于几乎所有人的预测。
该文可能具有重要的经济和地缘政治意义。如果中国和印度保持目前的增长轨迹，到2033年其国内生产总值(GDP)之和将从目前的11万亿美元，上升至66万亿美元。如果完全回归均值增速，到时中印GDP之和仅能达到24万亿美元。两位作者没有必要解释中国或（实际上）印度的增速为何应会如此陡峭下降。这不过就是目前发生的事情。他们的步步分析使得解释怎样才能不发生这种情况成为乐观者的责任。
有几种可以想象到的反驳理由。第一个适用于新兴市场的总体状况。“趋同”理念认为，贫穷国家可以比富国增长得更快。这部分是因为“低悬的果实”；例如，把人们从生产率低的农村工作，转向生产率更高的城市工作。穷国也可以学习模仿富国；它们不必重新发明轮子。哈佛大学(Harvard)历史学教授尼尔•弗格森(Niall Ferguson)提到了“繁荣的6大杀手级应用”：竞争、科学革命、财产权、医学、消费社会和职业道德。既然我们已知道它们是什么，就可以“下载”它们。包括日本、台湾、韩国和新加坡在内，几个亚洲经济体的生活水平或多或少都赶上了西方。如果它们能做到，为什么其他经济体不能？然而，回归均值意味着，如此迅速的追赶是不可能的，或者至少是非常困难的。
中国有没有什么特定因素表明它能够逆势而上？首先，中国已经做到了这一点，快速增长期超过了30年。两位经济学家说，这使得快速放缓的可能性变得更大。但也许会出现相反情况。中国领导人可能已经学会了如何战胜命运。第二，“金砖国家”(Brics)一词的发明者吉姆•奥尼尔(Jim O'Neill)说，两位作者的数据可能由于拉美、中东和非洲这些最令人失望的经济体而有所偏差。或许，亚洲经济体已经发现了一种独家秘方。第三，在中国的长期增长之前，是几十年的混乱和低水平增长。我们现在看到的，很可能真是一种被长期压抑之后的复苏——这是中国自己的回归均值过程。第四，中国的体量可能产生规模经济和国内市场规模方面的维持增长的优势。如果此情属实，这也适用于印度。（中国进出口网）
What would China look like if it were growing at just 2 per cent a year? That sounds like a ridiculously pessimistic question given China’s performance in the past three decades. Certainly, it has manifold problems. Indeed, its economy is already slowing. But what misadventure could possibly bring its growth rate crashing down so spectacularly?
That is the wrong question, according to an influential paper by US economists Lant Pritchett and Lawrence Summers . For them, “the single most robust and striking fact” about growth is “regression to the mean” of about 2 per cent. only rarely in modern history, they say, have countries grown at “super-rapid” rates above 6 per cent for much more than a decade. China has managed to buck the trend since 1977 by harnessing market forces, engineering possibly the longest spell “in the history of mankind”. But what goes up, the authors tell us, must eventually come down.
They have trawled through the data and drawn two powerful conclusions. One is that there is almost no statistical basis for predicting growth from one decade to another. Extrapolation is a mug’s game – or, as they put it, “current growth has very little predictive power”. From 1967 to 1980, Brazil grew at an average annual rate of 5.2 per cent. Few would have predicted, then, that for the next 22 years per capita income would grow at precisely zero.
Their second finding is that episodes of super-rapid growth last a median of nine years. China is the big exception. The only countries with fast-growth episodes that come close are Taiwan and South Korea, which managed 32 and 29 years respectively. According to the authors, once such episodes end, the median dro in growth is 4.65 points. That would cut China’s growth to 4 per cent and India’s to 1.6 per cent – far lower than almost anyone is predicting.
The thesis has huge potential ramifications, both economic and geopolitical. If China and India continue their current growth trajectories, their combined gross domestic product will rise to $66tn by 2033, against $11tn today. If they regressed fully to mean, they would reach a combined GDP of just $24tn. The authors have no need to explain why China’s, or indeed India’s, growth should fall so precipitously. This is just what happens. Their reasoning puts the onus on optimists to explain otherwise.
There are several conceivable rejoinders. The first applies to emerging markets generally. The idea of “convergence” holds that poor countries can grow faster than rich ones. That is partly because there is low-hanging fruit; for example, moving people from unproductive rural jobs to more productive urban ones. Poor countries can also copy rich ones; they do not have to reinvent the wheel. Niall Ferguson, professor of history at Harvard University, refers to “six killer apps of prosperity”: competition, scientific revolution, property rights, medicine, consumer society and the work ethic. Since we already know what they are, they can be “downloaded”. Several Asian economies, including Japan, Taiwan, South Korea and Singapore have more or less caught up with western living standards. If they can do it, why not others? Regression to mean, however, implies that such speedy catch-up is impossible, or at least very difficult.
Is there anything about China specifically that suggests it could buck the trend? First, it has already done so, growing rapidly for more than 30 years. The two economists say this makes a rapid slowdown more likely. But perhaps it is the reverse. Chinese leaders may have learnt how to beat the odds. Second, as Jim O’Neill, who coined the term Brics, says, the authors’ data may be skewed by the mostly disappointing economies of Latin America, the Middle East and Africa. Perhaps Asian economies have discovered a secret sauce. Third, China’s long-lived expansion follows many decades of chaos and suboptimal growth. What we are seeing now could plausibly be a long-pent-up recovery – the country’s own regression to mean. Fourth, China’s size could confer growth-sustaining advantages in terms of economies of scale and size of domestic market. If true, that would also apply to India.
