Quality Ladders and Product Cycles
构建了一个南北两国模型，研究内生创新与模仿的互动。北方企业竞相改进技术密集型产品，南方企业家投资学习北方技术，稳态均衡下创新与模仿率恒定，并分析区域规模和政策变化的影响。
We develop a two-country model of endogenous innovation and imitation in order to study the interactions between these two processes. Firms in the North race to bring out the next generation of a set of technology-intensive products. Each product potentially can be improved a countably infinite number of times, but quality improvements require the investment of resources and entail uncertain prospects of success. In the South entrepreneurs invest resources in order to learn the production processes that have been developed in the North. All R&D investment decisions are made by forward-looking, profit-maximizing entrepreneurs. The steady-state equilibrium is characterized by constant aggregate rates of innovation and imitation. We study how these rates respond to changes in the sizes of the two regions and to policies in each region to promote learning.