Basic Information

Position: Assistant Professor, The Information School
Adjunct Assistant Professor, Computer Science & Engineering
Director, Data Science and Analytics Lab
University of Washington
Contact: joshblum[@]uw[.]edu / +1 (206) 685-8746
for encrypted correspondence: my public key
My work focuses on the economic and social impacts of new technologies, and the development of new methods for the quantitative analysis of massive, spatio-temporal network data. Most of this work is based in developing and conflict-affected countries. I have open research positions for qualified PhD students.

News and updates

Recently Completed

Risk Sharing and Mobile Phones: Evidence in the Aftermath of Natural Disasters - joint with Marcel Fafchamps (Oxford) and Nathan Eagle (Santa Fe Institute)
We provide empirical evidence that an early form of "mobile money" is used to share risk. Our analysis uses a unique dataset containing the entire universe mobile phone-based communications over a four-year period in Rwanda, including millions of interpersonal transfers sent over the mobile phone network. Exploiting the quasi-random timing and location of natural disasters, we show that people send mobile money to individuals affected by economic shocks. Unlike other documented forms of risk sharing, the mobile-phone based transfers are sent over large geographic distances and in response to covariate shocks. Transfers are more likely to be sent to wealthy individuals, and are more consistent with a model of risk sharing where transfers are based on norms of reciprocity, rather than a naive model in which giving is based on pure charity. [View Video]
Understanding the causes and effects of internal migration is critical to the effective design and implementation of policies that promote human development. Here, we describe how large sources of geotagged data generated by mobile phones can provide a novel source of data on internal migration. We develop and formalize the concept of inferred mobility, and compute this and other metrics on a large dataset containing the phone records of 1.5 million Rwandans over four years. Our empirical results corroborate the findings of a recent government survey that notes relatively low levels of permanent migration in Rwanda. [View Video]
Expanding Rural Cellular Networks with Virtual Coverage - joint with Kurtis Heimerl, Kashif Ali, Brian Gawalt, and Eric Brewer
We present an alternative system for implementing large-scale rural cellular networks. Rather than providing constant coverage, we instead provide virtual coverage: coverage that is only present when requested. Virtual coverage powers the network on demand, which reduces overall power draw, lowers the cost of rural connectivity, and enables new markets.
This paper provides quantitative evidence of disparities in mobile phone access and use in Rwanda. Our analysis leverages data collected in 2,200 field interviews, which was merged with terabytes of transaction-level call histories obtained from the mobile telecommunications operator.

In the Field and Ongoing Projects

Violence and Precautionary Savings: Experimental Evidence from Mobile Phone-Based Salaries in Afghanistan - joint with Michael Callen (UCLA) and Tarek Ghani (UC Berkeley)
Private firms in conflict-affected countries face insecurity, corruption, poor infrastructure, and weak property rights. Disbursing employee wages is a challenge as cash-based payment systems are vulnerable to indirect costs in the form of leakage and theft. We implement a randomized field experiment in Afghanistan to test the effects of a mobile phone-based salary payment system on performance outcomes in a private firm with approximately 400 employees.
Freedom to Speak: How a Free Calling Network Affects Community Health Worker Knowledge and Productivity
We study the extent to which increased peer communication can improve the effectiveness of community health workers in Tanzania. Through a large field experiment in which roughly 8,000 health workers receive staggered access to a free mobile phone network, we measure the impact of this intervention on actual patterns of interaction and on health and welfare outcomes of workers and patients.
Savings in Conflict: The Impact of a Mobile Phone-Based Defined-Contribution Plan in Afghanistan - joint with Michael Callen (UCLA) and Tarek Ghani (UC Berkeley)
We study the extent to which a mobile phone-based defined contribution savings account can improve the financial capabilities and welfare outcomes of salaried employees at a large Afghan firm. Our research design uses a randomized controlled trial to understand whether a defined-contribution savings product can create an enduring increase in savings.
A Society of Silent Separation: The Impact of Migration on Ethnic Segregation in Estonia - joint with Ott Toomet (Tartu University)
We exploit a novel source of data to model the impact of migration and urbanization on segregation in Estonia. Analyzing the complete mobile phone records of hundreds of thousands of Estonians, we find that the ethnic composition of an individual's geographic neighborhood heavily influences the structure of the individual's phone-based network. We further find that patterns of segregation are significantly different for migrants than for the at-large population: migrants are more likely to interact with coethnics than non-migrants, but are less sensitive to the ethnic composition of their immediate neighborhood than non-migrants.