On the Frequency of Severe Terrorist Events

Journal of Conflict Resolution (Impact Factor: 2.24). 07/2006; 51(1). DOI: 10.1177/0022002706296157
Source: arXiv


In the spirit of Richardson's original (1948) study of the statistics of deadly conflicts, we study the frequency and severity of terrorist attacks worldwide since 1968. We show that these events are uniformly characterized by the phenomenon of scale invariance, i.e., the frequency scales as an inverse power of the severity, P(x) ~ x^-alpha. We find that this property is a robust feature of terrorism, persisting when we control for economic development of the target country, the type of weapon used, and even for short time-scales. Further, we show that the center of the distribution oscillates slightly with a period of roughly tau ~ 13 years, that there exist significant temporal correlations in the frequency of severe events, and that current models of event incidence cannot account for these variations or the scale invariance property of global terrorism. Finally, we describe a simple toy model for the generation of these statistics, and briefly discuss its implications.

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    • "Furthermore, it was implemented on poweRlaw package (Gillespie, 2014; Gillespie, 2015). The í µí±¥ � í µí±ší µí±–í µí±› value estimated is chosen in way that the estimated power law model gets a best fit of the empirical probability distribution for í µí±¥ ≥ í µí±¥ í µí±ší µí±–í µí±› (Clauset et al., 2007). Under the supposition that our data follows a power law for í µí±¥ ≥ í µí±¥ í µí±ší µí±–í µí±› ,, the α parameter is estimated by a numeric optimization of the log – likelihood. "
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    • "Power law probability distributions have the relatively simple form of p(x) ∝ x −α (1) where α > 1 and x > 0. The parameter α, is often referred to as the exponent or scaling parameter. Although straightforward, these distributions have gathered scientific interest from many areas, including terrorism, astrophysics, neuroscience, biology, database curation and criminology[7] [13] [1] [21] [2] [9]. "
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    • "As a consequence of these findings, researchers claimed that insurgent wars were qualitatively distinct from traditional wars. A coefficient value of ~ a ¼ 2:5 was in concordance with the coefficient value of ~ a ¼ 2:48 AE 0:07 obtained by Clauset et al. [38] on global terrorism. "
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