We provide empirical evidence that an early form of "mobile money" is used to transmit funds to individuals affected by catastrophic shocks. Contrasting two stylized models of prosocial behavior, we further provide insight into why people help each other in times of dire need. Our findings are based on the analysis of billions of mobile phone-based transactions that occur before and after a destructive earthquake in Rwanda. The observed pattern of transfers is not consistent with a model of pure charity or altruism, but better fits a model of instrumental reciprocity. This conclusion is supported by three distinct results. First, earthquake-induced transfers are increasing in the wealth of the recipient, and are not significantly related to the wealth of the sender. Second, transfers sent in response to the earthquake are highly dependent on the prior history of transfers. Third, transfers decrease as the distance between sender and recipient increases, even after controlling for the strength of pairwise relationships. Taken together, the evidence indicates that Rwandans use the mobile phone network to help afflicted friends and family, but that these gifts are motivated, at least in part, by a desire for reciprocity. [View Video]

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 detailed transaction-level call histories obtained from the mobile telecommunications operator. We present three related results. First, comparing the population of mobile phone owners to the general Rwandan population, we find that phone owners are considerably wealthier, better educated, and more predominantly male. Second, based on self-reported data, we observe statistically significant differences between genders in phone access and use; for instance, women are more likely to use shared phones than men. Finally, analyzing the complete call records of each subscriber, we note large disparities in patterns of phone use and social network structure by socioeconomic status. Taken together, the evidence in this paper suggests that phones are disproportionately owned and used by the privileged strata of Rwandan society.

Understanding the causes and effects of internal migration is critical to the effective design and implementation of policies that promote human development. In this paper, we describe how new information and communications technologies, and mobile phones in particular, 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. However, our analysis reveals more subtle patterns that were not detected in the government survey. Namely, we observe high levels of temporary and circular migration, and note significant heterogeneity in mobility within the Rwandan population. [View Video]