Quality Ladders in the Theory of Growth
构建了一个多部门连续产品改进模型，每个产品沿质量阶梯随机升级，非均衡进步导致质量分布随时间演变，但总增长率恒定，并受研发部门利润激励影响。
The authors develop a model of repeated product improvements in a continuum of sectors. Each product follows a stochastic progression up a quality ladder. Progress is not uniform across sectors, so an equilibrium distribution of quality evolves over time. But the rate of aggregate growth is constant. The growth rate responds to profit incentives in the R&D sector. The authors explore the welfare properties of the model. Then they relate their approach to an alternative one that views product innovation as a process of generating an ever-expanding range of horizontally differentiated products. Finally, the authors apply the model to issues of resource accumulation and international trade. Copyright 1991 by The Review of Economic Studies Limited.