CSTPR Noontime Seminar: Estimating the Historical and Future Probabilities of Large Terrorist Events
ESTIMATING THE HISTORICAL AND FUTURE PROBABILITIES OF LARGE TERRORIST EVENTS
by Aaron Clauset, Department of Computer Science, University of Colorado Boulder
CIRES S274, University of Colorado Campus
Free and open to the public
Abstract: Quantities with right-skewed distributions are ubiquitous in complex social systems, including political conflict, economics and social networks, and these systems sometimes produce extremely large events. For instance, the 9/11 terrorist events produced nearly 3000 fatalities, nearly six times more than the next largest event in the past 40 years. But, was this enormous loss of life statistically unlikely given modern terrorism's historical record? Accurately estimating the probability of such an event is complicated by the large fluctuations in the empirical distribution's upper tail.
In this talk, I present a generic statistical algorithm for making such judgements, which combines semi-parametric models of tail behavior and a non-parametric bootstrap. Applied to a global database of terrorist events, the method estimates the worldwide historical probability of observing at least one 9/11-sized or larger event since 1968 to be 11–35%. These results remain even when we condition on global variations in economic development, domestic versus international events, the type of weapon used and a truncated history that stops at 1998. I will also show results for using this technique to make a data-driven statistical forecast of at least one similar event over the next decade. To close, I will briefly discuss the applicability of this technique to other complex systems with heavy-tailed distributions of event sizes.
Joint work with Ryan Woodard (ETH Zurich).
Biography: Aaron Clauset received a PhD in Computer Science from the University of New Mexico and a BS in Physics from Haverford College, and was an Omidyar Fellow at the prestigious Santa Fe Institute.
Clauset is an internationally recognized expert on complex networks, complex systems, the statistics of rare events, global patterns in terrorism and war. His work has appeared in prestigious scientific venues like Nature, Science, JACM, STOC, AAAI, SIAM Review, Physical Review Letters, and the Journal of Conflict Resolution, and has been covered in the popular press by the Wall Street Journal, The Economist, Discover Magazine, New Scientist, Miller-McCune, the Boston Globe and The Guardian.