  Existing theories of gun violence predict stable spatial concentrations and
contagious diffusion of gun violence into surrounding areas. Recent empirical
studies have reported confirmatory evidence of such spatiotemporal diffusion of
gun violence. However, existing tests cannot readily distinguish spatiotemporal
clustering from spatiotemporal diffusion. This leaves as an open question
whether gun violence actually is contagious or merely clusters in space and
time. Compounding this problem, gun violence is subject to considerable
measurement error with many nonfatal shootings going unreported to police.
Using point process data from an acoustical gunshot locator system and a
combination of Bayesian spatiotemporal point process modeling and space/time
interaction tests, this paper demonstrates that contemporary urban gun violence
does diffuse, but only slightly, suggesting that a disease model for infectious
spread of gun violence is a poor fit for the geographically stable and
temporally stochastic process observed.
