Knowledge Spillovers and Inequality
构建了一个包含知识溢出的动态模型，发现模仿他人虽能帮助追赶，但搭便车效应占优，导致持久不平等；溢出越强、越易获得，搭便车和不平等越严重，且定向复制会加剧不平等。
We develop a dynamic model with knowledge spillovers in production. The model contains two opposing forces. Imitation of other firms helps followers catch up with leaders, but the prospect of doing so makes followers want to free ride. The second force dominates and creates permanent inequality. We show that the greater are the average spillovers and the easier they are to obtain, the greater is the free-riding and inequality. More directed copying raises inequality by raising the free-riding advantages of hanging back. Using Compustat and patent-citation data we find that copying is highly undirected.