THE ADOPTION OF NETWORK GOODS: EVIDENCE FROM THE SPREAD OF MOBILE PHONES IN RWANDA DANIEL BJÖRKEGREN∗ BROWN UNIVERSITY This paper 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 net- works, 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 oper- ator 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 3.11 times the revenue raised. Shift- ing from handset to usage taxes would have increased the surplus of poorer users by at least 26%. JEL Classification Codes: O33, L96, O180, L51 Keywords: network goods, infrastructure, information technology ∗E-mail:
[email protected], Web: http://dan.bjorkegren.com Revision January 3, 2018. I am grateful to Michael Kremer, Greg Lewis, and Ariel Pakes for guidance and encouragement. Thank you to Nathan Eagle for providing access to the data, computing facilities, and helpful conversations. For helpful conversations I am also grateful to Natalie Bau, Arun Chandrasekhar, Brian Dillon, Michael Dinerstein, Ben Golub, Rick Hornbeck, Sabrina Howell, Max Kasy, Divya Kirti, Daniel Pollmann, Martin Rotemberg, Heather Schofield, Jesse Shapiro, Mark Shepard, Rob Stewart, Laura Trucco, and Tom Zimmerman.