Optimum Product Diversity and the Incentives for Entry in Natural Oligopolies
研究自然寡头市场中垄断竞争均衡与计划者最优的产品种类偏差，发现若产品为替代品则种类不会过少、可能过多；若为互补品则种类不会过多、可能过少。
This paper concerns the classification of biases in the set of produced varieties in a monopolistically competitive equilibrium in the natural oligopoly setting. That is, we analyze the relationship between the set of produced goods in equilibrium when fixed costs are small and the set of produced goods by a social planner when fixed costs equal zero. It is shown that if all of the goods are substitutes, there are never too few varieties, and there may be too many. Conversely, if the goods are all complementary, there are never too many, and there may be too few.