title: Terrorist attacks escalate in frequency and fatalities preceding highly lethal attacks.
abstract: Highly lethal terrorist attacks, which we define as those killing 21 or more people, account for 50% of the total number of people killed in all terrorist attacks combined, yet comprise only 3.5% of terrorist attacks. Given the disproportionate influence of these incidents, uncovering systematic patterns in attacks that precede and anticipate these highly lethal attacks may be of value for understanding attacks that exact a heavy toll on life. Here we examined whether the activity of terrorist groups escalates--both in the number of people killed per attack and in the frequency of attacks--leading up to highly lethal attacks. Analyses of terrorist attacks drawn from a state-of-the-art international terrorism database (The Global Terrorism Database) showed evidence for both types of escalation leading up to highly lethal attacks, though complexities to the patterns emerged as well. These patterns of escalation do not emerge among terrorist groups that never commit a highly lethal attack.
authors.affiliation: University of Canterbury, Christchurch, New Zealand.
authors.forename: Andy
authors.initials: A
authors.lastname: Martens
authors.affiliation: University of Canterbury, Christchurch, New Zealand.
authors.forename: Raazesh
authors.initials: R
authors.lastname: Sainudiin
authors.affiliation: University of Auckland, Auckland, New Zealand.
authors.forename: Chris G
authors.initials: CG
authors.lastname: Sibley
authors.affiliation: University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Jeff
authors.initials: J
authors.lastname: Schimel
authors.affiliation: University of Alberta, Edmonton, Alberta, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Webber
mesh_terms: D006801:Humans; D054527:Mass Casualty Incidents; D008962:Models, Theoretical; D023481:Terrorism
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