If economics can tell us something useful about crime, marriage or car-pooling – as I believe it can – then other academic disciplines should have something to tell us about economies. Last month, Science published an example that may turn out to be important. Two physicists¹, Cesar Hidalgo and Albert-Laszlo Barabasi, and two economists², Bailey Klinger and Ricardo Hausmann, have been drawing unusual pictures of economic “space” that promise a deeper understanding of the biggest question in economics: why poor countries are poor.

这个问题有很多解释，但其中一些比另一些更容易检验。对于为什么一些贫穷国家会贫穷的原因，一个非常可信的理由是，从当前状态向富裕状态的转变过程并不平坦。举例来说，从开采石油到制造硅芯片可能需要同时在教育、交通基础设施、电力以及许多其它方面进行投资。对于私营企业来说，如果没有政府的某种协调努力——“大推进”(big push)，那么这一鸿沟可能无法跨越。这是经济学中一种古老而直观的观点，但作为一种非正式的论点，它有很多不足之处。首先，尽管看似可信，但它可能并不正确。即使它是正确的，那么它可能更适用于某些类型的经济体，而对另一些经济体则不那么适用。另外，如果政府要实行大推进，那么它应当对准哪个方向呢？ There are many explanations, but some are easier to test than others. One very plausible³ account of why at least some poor countries are poor is that there is no smooth progression from where they are to where they would be when rich. For instance, to move from drilling oil to making silicon⁴ chips might require simultaneous investments in education, transport infrastructure⁵, electricity and many other things. The gap may be too wide for private enterprise to bridge without some sort of co-ordinating effort from government – a “big push”. That is an old and intuitive idea in economics, but as an informal argument it leaves a lot to be desired. For a start, while plausible, it might not be true. If it is true, it might be far more so for some kinds of economy than for others. And if there is to be a big push, in which direction should it go?

检验这一观点需要三个步骤。首先，美国国家经济研究局(National Bureau of Economic Research)的经济学家将每个国家的出口分成775种不同的产品。然后，奥斯曼和科林格用这些数据衡量每一种产品与另一种产品的相似度。如果每个主要的苹果出口国也出口梨，每个主要的梨出口国也出口苹果，那么这些数据就会显示，苹果和梨是相似的。推测看来，两个国家都应该拥有肥沃的土壤、农艺学家、冷冻包装工厂和港口。

Testing the idea took three steps. First, economists at the National Bureau of Economic Research, in the US, broke down each country’s exports into 775 distinct products. Next, Hausmann and Klinger used that data to measure how similar each product is to each other product. If every major apple exporter also exports pears, and every major pear exporter also exports apples, then the data are demonstrating apples and pears to be similar. Presumably, both economies would have fertile soil, agronomists⁶, refrigerated packing plants and ports.

至于第三步，奥斯曼和科林格拜访了擅长绘制和分析网络的伊达尔戈和鲍劳巴希。结果就是一幅抽象经济学空间中不同产品之间的关系图。苹果和梨非常接近，而石油生产则与其它任何东西都相去甚远。

For the third step, Hausmann and Klinger called upon Hidalgo and Barabasi, who specialise in mapping and analysing networks. The result was a map of the relationships between different products in an abstract economic space. Apples and pears are close together, oil production is a long way away from anything else.

通过突出每个国家出口的产品，两位物理学家展示了每个经济体在这个产品网络中的位置。从长期看，随着经济体出口组合的变化，它们会沿着产品图移动。富裕国家拥有更大、更多样化的经济，因此能够生产大量产品——尤其是那些与紧密相连的网络中心非常近的产品。东亚经济体看上去差别很大，一部分国家集中在纺织品附近，还有一部分国家集中在电子制造周围。此外，与炒作的情况相反，该地区很少产出富裕国家所制造的产品。非洲国家生产的产品往往与其它国家没有太多相似之处。

The physicists’ map shows each economy in this network of products, by highlighting the products each country exported. Over time, economies move across the product map as their export mix changes. Rich countries have larger, more diversified⁷ economies, and so produce lots of products – especially products close to the densely⁸ connected heart of the network. East Asian economies look very different, with a big cluster around textiles and another around electronics manufacturing, and – contrary to the hype – not much activity in the products produced by rich countries. African countries tend to produce a few products with no great similarity to any others.

这可能是一个大问题。这些网络图显示，经济体往往沿着紧密关联的产品发展。哥伦比亚等国生产在网络上联系紧密的产品，因此，如果商业环境的其它条件允许的话，私营企业就有大量进入机会。但南非现在的许多出口产品——例如钻石——与任何东西都不太相似。如果该国开发新产品，将意味着实现大跳跃。数据显示，这种跳跃不经常发生。

That could be a big a problem. The network maps show that economies tend to develop through closely related products. A country such as Colombia makes products that are well connected on the network, and so there are plenty of opportunities for private firms to move into, provided other parts of the business climate allow it. But many of South Africa’s current exports – diamonds, for example – are not very similar to anything. If the country is to develop new products, it will mean making a big leap. The data show that such leaps are unusual.

这些都不能证明，包括提供融资、打击腐败、减少官僚主义和降低贸易壁垒在内的其它经济发展药方是无用的。它也并非为粗暴的产业政策开了绿灯。科林格提醒道：“人们很容易把政策含意理解得过远，开始尝试在产品空间中挑选栖身之地。”但这是一大进步。政策制定者应当注意，经济学家也是。

None of this is proof that other development prescriptions⁹ – provide finance, fight corruption¹⁰, cut red tape and lower trade barriers – are useless. Nor is it a green light for hamfisted industrial policy. Klinger warns: “It’s easy to take the policy implication too far and start trying to pick and choose where to settle in the product space.” But it is a big step forward. Policymakers should take note, and economists, too