Why are Some Countries Richer than Others? Intermediate Goods and Weak Links in the Theory of Economic Development

到20世纪末，美国的人均收入比埃塞俄比亚和扎伊尔的人均收入高出50多倍。如何解释各国之间如此巨大的收入差异？在最近的经济学文献中，产权、腐败和激励的差异被怀疑是原因。但在标准模型中，这些维度上的差异通常会导致10倍的收入差异，而不是我们在数据中观察到的50倍差异。本项目开发了一个模型，其中中间产品提供了部门之间的联系，从而产生乘数效应。例如，发电行业的腐败降低了该行业的产出，进而降低了依赖电力作为投入的银行和建筑行业的产出。但这降低了电力行业建造新水坝的难度，因此进一步降低了发电量。这种乘数效应类似于标准增长模型中与资本积累相关的乘数。但是，由于中间产品占收入的份额约为1/2，因此中间产品乘数很大。初步分析表明，这些因素确实能够解释各国之间收入的巨大差异。在生产自行车或毛衣方面，肯尼亚一家典型的公司可能只有美国一家典型公司的一半左右。但肯尼亚企业的人均产出可能比美国低32倍，因为电力、铝管和橡胶轮胎等中间投入也是以这1/2的效率生产的。这就是中间产品乘数在起作用。研究还试图解释为什么解决经济发展问题被证明是如此困难。这里的解释与互补性有关，即一条链条的强度取决于它最薄弱的环节。企业的高生产率要求在许多方面都有高水平的绩效。纺织品生产商需要原材料、针织机、健康和训练有素的劳动力、生产知识、安全、营业执照、产权、运输网络、电力等。这些输入以互补的方式进入，就像链条上的薄弱环节。任何方面的问题都会大大降低总产量：没有电力、生产知识、原材料、安全或营业执照，生产都可能受到严重阻碍。在世界上最贫穷的国家，问题可能同时在许多方面出现。因此，只解决一个或两个方面的改革可能对整体经济表现的影响很小。更广泛的影响与经济增长和发展有关的问题是当今世界最重要的经济政策问题之一。理解为什么在世界上最富裕的国家导致巨大财富的经济力量在最贫穷的国家却缺失，提供了一个巨大的机会。

By the end of the 20th century, per capita income in the United States was more than 50 times higher than per capita income in Ethiopia and Zaire. What explains such profound differences in incomes across countries?In the recent economics literature, differences in property rights, corruption, and incentives are suspected as causes. But in standard models, differences along these dimensions typically lead to 10-fold income differences rather than the 50-fold differences we observe in the data. This project develops a model in which intermediate goods provide links between sectors that create a multiplier effect. For example, corruption in electric power generation reduces output in that sector, which in turn reduces output in banking and construction -- sectors that rely on electricity as an input. But this reduces the ease with which the electricity industry can build new dams and therefore further reduces output in electric power generation. This multiplier effect is similar to the multiplier associated with capital accumulation in a standard growth model. However, because the intermediate goods' share of revenue is approximately 1/2, the intermediate goods multiplier is large. Preliminary analysis suggests that these forces will indeed be able to explain enormous differences in incomes across countries.A typical firm in Kenya may be roughly half as good as a typical firm in the United States at producing bicycles or sweaters. But output per worker in Kenyan firms may be 32 times lower than in the United States because intermediate inputs like electricity, aluminum tubes, and rubber tires are also produced with this 1/2 efficiency. This is the intermediate goods multiplier at work.The research also attempts to explain why solving the economic development problem has proved to be so difficult. Here, the explanation is related to complementarity --- the notion that a chain is only as strong as its weakest link. High productivity in a firm requires a high level of performance along many dimensions. Textile producers require raw materials, knitting machines, a healthy and trained labor force, knowledge of how to produce, security, business licenses, property rights, transportation networks, electricity, etc. These inputs enter in a complementary fashion, like the weak links in a chain. Problems along any dimension can substantially reduce overall output: Without electricity or production knowledge or raw materials or security or business licenses, production is likely to be severely hindered. In the poorest countries of the world, problems may occur along many dimensions at once. Reforms that address only one or two dimensions, then, may have small effects on overall economic performance. Broader ImpactsQuestions related to economic growth and development are among the most important economic policy issues in the world today. Understanding why the economic forces that lead to enormous wealth in the richest countries of the world are absent in the poorest offers a tremendous opportunity.