To think that two and two are four / And neither five nor three / The heart of man has long been sore / And long ‘tis like to be. A.E. Housman.
想到二加二等于四/而不是五也不是三/人心早已满怀酸楚/往后也没有尽头 A.E.豪斯曼(A.E. Housman)
In 1810, 81 per cent of the US labour force worked in agriculture, 3 per cent worked in manufacturing and 16 per cent worked in services. By 1950, the share of agriculture had fallen to 12 per cent, the share of manufacturing had peaked, at 24 per cent, and the share of services had reached 64 per cent. By 2020, the employment shares of these three sectors reached under 2 per cent, 8 per cent and 91 per cent, respectively. The evolution of these shares describes the employment pattern of modern economic growth. It is broadly what happens as countries become richer, whether they are big or small or run trade surpluses or deficits. It is an iron economic law.
1810年，美国81%的劳动力做农业工作，3%做制造业工作，而16%做服务业工作。到1950年，农业就业的比重已经降至12%，制造业就业的比重已经见顶，达到24%，而服务业就业比重达到64%。到2020年，这三个产业的就业比重分别为不足2%、8%和91%。这些比重的演化体现了现代经济增长的就业模式。这是国家变富裕时通常会发生的情况，不论是大国还是小国，存在贸易顺差还是逆差。这是经济铁律。
What drives this evolution? In Behind the Curve — Can Manufacturing Still Provide Inclusive Growth?, Robert Lawrence of Harvard’s Kennedy School and the Peterson Institute for International Economics (PIIE) explains it in terms of a few numbers — the initial shares of employment in each of the three sectors, “income elasticities of demand” for their products, their “elasticities of substitution” and relative rates of growth of productivity. Income elasticities measure the proportional increase in demand for a category of goods or services relative to income. Elasticities of substitution measure the impact of changes in price on demand. A crucial consequence of the simple model that emerges is “spillovers”: what happens to a sector also depends hugely on what happens in the other sectors.
驱动这一演化的是什么？在《曲线背后——制造业还能提供包容性增长吗？》(Behind the Curve — Can Manufacturing Still Provide Inclusive Growth?)中，哈佛大学肯尼迪学院(Harvard Kennedy School)和彼得森国际经济研究所(Peterson Institute for International Economics)的罗伯特•劳伦斯(Robert Lawrence)用几个数字做了解释——三个产业各自的初始就业比重，其产品的“需求收入弹性”，它们的“替代弹性”，以及生产力增长的相对速度。收入弹性衡量的是一个商品或服务品类的需求数量与收入的相对增长率。替代弹性衡量的是价格变化对需求的影响。这个简单模型产生的一个关键结果就是“溢出”：一个产业的情况也很大程度取决于其他产业的情况。