Detecting emerging risks of drug-related crimes

Background: Drug-related crimes are known to form patterns of concentration, persistence and recurrence over space and time. Rapid and accurate identification of emerging hotspots constitutes a key element in policing effort to reduce drug-related crimes. However, most of the existing methods are less effective in pinpointing the hotspot locations or lack the capacity to detect emerging risks in near-real time. Methods: A conceptual framework of a network-based geosurveillance method has been recently proposed for the purpose of monitoring elevated activities recorded at the disaggregate, micro-scale level of street addresses. It extends the notion of syndromic surveillance in epidemiology by introducing a flexible space-time search window that sweeps repeatedly along street networks as new incidents are reported. This paper applies this method for detecting emerging micro-scale drug hotspots and explores its validity as a means to aid hotspot policing. Empirical data are used for exploring the space-time signature of drug hotspots, while simulated data are introduced for testing the effectiveness of geosurveillance in detecting emerging hotspots accurately. Results: Empirical analysis highlighted that drug hotspots do not conform to one specific pattern of space-time signature but rather consist of a mixture of recurrent hotbeds and one-off outbursts with a varying rate of growth and frequency. Performance test showed that network-based geosurveillance detects emerging drug hotspots more accurately than its conventional counterpart can. It is sensitive to both an early sign of slowly emerging risks as well as sudden outbursts of crime, and detects them without over- or under-representing their locations. Conclusion: The results suggest that network-based geosurveillance offers an effective means to accurately detect emerging drug hotspots, thus enabling targeted intervention by the local law enforcement. Its capacity to give out early warning allows for a tactical solution of rapid and pinpointed intervention, whilst its ability to detect recurrent hotbeds facilitates a more strategic approach to change the environment and situations around those locations