Variety-Based Congestion in Online Markets: Evidence from Mobile Apps
利用安卓应用商店的自然实验，发现应用数量增加会降低单个应用的使用和下载量，即存在拥挤外部性；结构模型表明消费者品种福利的40%因拥挤而损失。
In many online markets, consumers have to spend time and effort browsing through products. The addition of new products could make other products less visible, creating congestion externalities. Using Android app store data, I take advantage of a natural experiment—a redesign of part of the store—to show evidence of congestion externalities online: more apps in the market directly reduce per app usage/downloads. The natural experiment also increases long-run entry, but a structural demand model that accounts for congestion externalities suggests that 40 percent of consumer variety welfare gains are lost from higher congestion.