Population, Ideas, and Economic Growth

该提案中概述的研究项目是由两个经验事实驱动的：在过去125年中，美国人均收入增长率没有任何明显的趋势，以及在一百万年的历史中，世界人口增长率加速，从平均略高于零到目前每年约2%的速度。第一个事实是卡尔多（Kaldor，1961）所表达的观点的基础，并体现在许多增长模型中，即平衡的稳态增长是我们的模型应该匹配的一个关键事实。第二个项目则相反：至少在世界历史的大部分时间里，人口增长--或许还有人均收入增长--绝非稳定。本项目的第一个项目将提出一个经济增长的一般理论，其中人均收入增长和人口增长紧密相连。正如最近的许多论文所述，经济增长是因为知识存量的增长。然而，该理论进一步表明，知识存量的增长是因为思想的发明者--人的存量的增长。内生人口增长和规模报酬递增是内生增长理论的两个关键要素。第二个项目考察了这一基本理论在多大程度上能够定量地解释这两个事实。最近的几位作者，如Klenow和Rodriguez-Clare（1997）以及McGravity和Schmitz（1998）指出，令人惊讶的是，很少有人研究新增长理论模型的定量含义，也很少有人试图区分这些模型;这个项目是朝着这个方向迈出的一步。第一个应用程序将使用新的增长理论框架对20世纪世纪美国的增长进行增长核算。初步结果表明，美国近期增长中只有约1/4与长期增长有关（世界人口增长）;其余3/4似乎是模仿平衡增长路径出现的暂时性因素的结果。第二个应用将把土地加入内生生育力/思想框架，并认为克雷默（1993）研究的人口证据最后，第三个项目将考察新思想的生产函数的形状，这在新增长理论中起着关键作用。对这一生产函数的初步探索强化了平衡增长不太可能发生的观点，这一提议的结果对大部分增长理论中的隐含假设提出了质疑，部分原因是卡尔多程式化的事实，即我们的模型应该永远产生持续的平衡增长。

The research projects outlined in this proposal are motivated by two empirical facts: the lack of any clear trend in U.S. per capita income growth rates during the last 125 years and the acceleration of world population growth rates throughout a million years of history, from rates averaging only slightly more than zero to the present rates of around two percent per year. The first fact underlies the view expressed by Kaldor (1961) and embodied in many growth models that balanced, steady-state growth is a key fact our models should match. The second suggests the opposite: at least for the bulk of world history, population growth-and presumably per capita income growth as well-is anything but steady.The first project in this proposal will suggest a general theory of economic growth in which per capita income growth and population growth are tightly linked. As in many recent papers, economies grow because of growth in the stock of knowledge. However, the theory goes further to suggest that the stock of knowledge grows because of growth in the stock of people, the inventors of ideas. Endogenous population growth and the increasing returns to scale that results from the nonrivalry of ideas are viewed as the two key ingredients of a theory of endogenous growth.The second project examines the extent to which this basic theory can explain quantitatively the two facts that motivate the proposal. Several recent authors such as Klenow and Rodriguez-Clare (1997) and McGrattan and Schmitz (1998) note that there is surprisingly little work designed to examine the quantitative implications of the models of new growth theory and to attempt to distinguish among these models; this project is a step in this direction. The first application will conduct a growth accounting exercise for 20th century U.S. growth using a new growth theory framework. Preliminary results suggest that only about 1/4 of recent U.S. growth is associated with the long-run component (world population growth); the remaining 3/4 seems to be the result of transitory factors that mimic the appearance of a balanced growth path. The second application will add land to the endogenous fertility/ideas framework and argue that the population evidence examined by Kremer (1993) can be understood as one long transition path.Finally, the third project will examine the shape of the production function for new ideas, which plays a key role in new growth theory. Preliminary exploration of this production function reinforces the notion that balanced growth is unlikely to occur.The results from this proposal raise questions about the implicit assumption in much of growth theory, motivated partly by the Kaldor stylized facts, that our models should generate sustained, balanced growth forever.