The Adoption of Network Goods: Evidence from the Spread of Mobile Phones in Rwanda
利用卢旺达近全部手机用户的交易数据，估计手机需求受社交网络、覆盖和价格的影响，并模拟政策效果：农村覆盖要求降低运营商利润但提高净社会福利；忽视网络效应的税收成本低估高达3.12倍，从手机税转向使用税可使贫困用户剩余增加至少26%。
This article develops a method to estimate and simulate the adoption of a network good. I estimate demand for mobile phones as a function of individuals’ social networks, coverage, and prices, using transaction data from nearly the entire network of Rwandan mobile phone subscribers at the time, over 4.5 years. I estimate the utility of adopting a phone based on its eventual usage: subscribers pay on the margin, so calls reveal the value of communicating with each contact. I use this structural model to simulate the effects of two policies. A requirement to serve rural areas lowered operator profits but increased net social welfare. Developing countries heavily tax mobile phones, but standard metrics that neglect network effects grossly understate the true welfare cost in a growing network, which is up to 3.12 times the revenue raised. Shifting from handset to usage taxes would have increased the surplus of poorer users by at least 26%.