Innovating Firms and Aggregate Innovation
构建了一个简洁的创新模型，统一分析企业、行业和总体经济，解释了企业研发投入的持续性、研发集中在现有企业、研发与专利的关系，以及研发占收入比与生产率正相关但与规模或增长无关的现象。
We develop a parsimonious model of innovation to confront firm‐level evidence. It captures the dynamics of individual heterogeneous firms, describes the behavior of an industry with firm entry and exit, and delivers a general equilibrium model of technological change. While unifying the theoretical analysis of firms, industries, and the aggregate economy, the model yields insights into empirical work on innovating firms. It accounts for the persistence of firms’ R&D investment, the concentration of R&D among incumbents, the link between R&D and patenting, and why R&D as a fraction of revenues is positively correlated with firm productivity but not with firm size or growth.