A Department of Homeland Security Center of Excellence led by the University of Maryland

Modeling Risk of Future Terrorist Attacks

Modeling Risk of Future Terrorist Attacks


Project Details


This project builds on existing data in the Global Terrorism Data base to allow analysis of (1) global aerial hijackings and (2) terrorist incidents in Northern Ireland.  We use the GTD to examine global patterns of terrorist strikes, group dynamics of terrorist organizations, and the impact of counter-terrorism activities.  Overall, we find that tactical interventions by law enforcement (metal detectors) and the legal prescriptions against terrorism reduced the frequency of some types of terrorism (hijackings), but were not effective against other attack types or sometimes led to subsequent increases in terrorism (as found in Northern Ireland).

Primary Findings: 

This project pursued two main research themes, both directed at gauging the success of counter measures used by governments to control terrorism. First, we used data from the GTD, the Federal Aviation Administration, and the RAND Corporation to develop a data base of 1,101 attempted aerial hijackings that occurred around the world from 1931 to 2003. We found support for the conclusion that new hijacking attempts were less likely to be undertaken when the certainty of apprehension was increased through metal detectors and law enforcement at passenger checkpoints. We also found that fewer hijackers attempted to divert airliners to Cuba once that country made it a crime to hijack flights. Our results support the contagion view that hijacking rates significantly increase after a series of hijackings closely clustered in time -- but only when these attempts were successful. We found that the policy interventions examined here significantly decreased the likelihood of non-terrorist hijackings but not that of terrorist hijackings. Second, we conducted a study on republican terrorism in Northern Ireland aimed at determining the impact of a set of counter measures tried by the British over time. This research showed that two criminal justice interventions, targeted assassinations, and a major military curfew either had no impact on subsequent terrorist strikes or significantly increased them. By contrast, a military surge called "Operation Motorman" had a significant impact on reducing future terrorist attacks by the IRA and its affiliates.


For the hijacking study we use continuous-time survival analysis to estimate the impact of several major counter hijacking interventions on the hazard of differently motivated hijacking attempts and logistic regression analysis to model the predictors of successful hijackings. For the study of countermeasures in Northern Ireland we use hazard modeling.


Project Period: 
May 2005 to June 2009