Scale Invariance in Global Terrorism

TL;DR

This paper demonstrates that the severity of global terrorist attacks follows a scale-free distribution with a consistent exponent over decades, indicating an inherent scale invariance in terrorism severity.

Contribution

It applies extremal statistics to global terrorism data, revealing a robust scale-free pattern in attack severity that persists over time and across different contexts.

Findings

Attack severity follows a scale-free distribution with an exponent near two.

The scale invariance property remains stable over 37 years.

Distribution of attack sizes has changed little over time.

Abstract

Traditional analyses of international terrorism have not sought to explain the emergence of rare but extremely severe events. Using the tools of extremal statistics to analyze the set of terrorist attacks worldwide between 1968 and 2004, as compiled by the National Memorial Institute for the Prevention of Terrorism (MIPT), we find that the relationship between the frequency and severity of terrorist attacks exhibits the ``scale-free'' property with an exponent of close to two. This property is robust, even when we restrict our analysis to events from a single type of weapon or events within major industrialized nations. We also find that the distribution of event sizes has changed very little over the past 37 years, suggesting that scale invariance is an inherent feature of global terrorism.