Growth, Entry and Exit of Firms
构建了一个行业均衡的动态模型，解释企业进入与退出同时发生的原因，并说明在完全竞争和规模报酬不变下超额利润为何能长期存在。
A dynamic model of industry equilibrium is presented which shows how growth, entry and exit of firms are interrelated. By taking into account the fact that a firm's profitability is to some degree subject to random shocks, the simultaneous occurrence of entry and exit can be explained formally. In addition, by also taking internal growth costs into account, it is shown that excess profits can persist in long-run equilibrium even in perfect competition and with constant returns to scale. The model is consistent with the facts that industry growth comes mainly from existing firms and that most firms grow at rates which do not systematically depend on their scale of operations. I. Introduction