A Situational Model of Displacement and Diffusion Following the Introduction of Airport Metal Detectors

Much of the discourse surrounding counterterrorism centers on the inevitability of displacement, or the substitution of another form of terrorist attack in place of the one that has been thwarted. Yet a longstanding tradition of research in situational crime prevention finds that displacement is far from inevitable, and often depends crucially on the specific features of the incidents in question. In fact, crime prevention efforts are often followed by a “diffusion of benefits” (i.e., crime reductions) to incidents, groups, or locations that were not the intended target of the intervention. The current study examines various forms of displacement and diffusion in response to airport metal detectors among terrorist groups that had been involved in the perpetration of aviation attacks prior to their implementation. Using data from the Global Terrorism Database, the findings from interrupted time series models suggest a complex set of displacement and diffusion effects with respect to alternative attack modes, target types, and weapon usage.