This paper examines the impact of mobile phone coverage on insurgent violence. In theory, access to coverage can lower violence by increasing the flow of information from civilians to the government and by shielding informers from retaliation. On the other hand, cell phone access can increase violence by reducing the cost of producing violence (e.g., facilitating coordination among insurgents, remote detonation of IEDs). To answer this question, we propose a novel method that can be employed by researchers studying the impact of mobile phone coverage of any outcome of interest. Specifically, we estimate a high spatial resolution radio-wave propagation model that uses variations in terrain topography and the spatial distribution of mobile phone towers to predict signal strength on the ground for each cell of a 1X1 kilometer grid of Afghanistan. The predicted signal strength is then used in a regression discontinuity design that compares grid cells within a small bandwidth around the signal strength threshold required for coverage. At this margin, access to coverage is mostly determined by minor exogenous changes in terrain features that lead to arbitrary diffractions and blocking of the signal. We find considerable evidence that the net effect of access to mobile phone technology is to lower insurgent violence. Specifically, grid cells with just enough coverage experience a 2 percentage point drop in the likelihood of any attack and a 0.8 percentage point drop in the likelihood of an IED. This effect remains robust even in areas where community norms are favorable to insurgents. Further analysis suggests that information gathering is likely a key mechanism. The deterring effect of coverage is significantly larger in cells where detection of insurgent activities by civilians is more likely: near populated areas, near primary roads, and during morning hours. Similarly, the effect of coverage on the failure rate of attacks–measured as the share of unsuccessful IEDs–significantly increases in these cells.
Keywords: cell phone access, insurgent violence, spatial regression discontinuity