Article Correctness Is Author's Responsibility: Some TRAP-18 indicators discriminate between terrorist attackers and other subjects of national security concern.

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The Terrorist Radicalization Assessment Protocol (TRAP-18) was utilized to code 2 nonrandom samples of convenience: Subjects who had carried out a lethal terrorist attack in North America between 1993 and 2016 (n = 33), and subjects who were identified as a national security concern, and were either successfully risk managed for at least 2 years, or determined upon investigation to have no intent to mount an attack, were not risk managed, and did not mount an attack during the same period of time (n = 23). The no attack sample was gathered from 2 metropolitan areas in the United States and Canada through law enforcement and mental health counterterrorism investigations. Half the TRAP-18 indicators were found to be significantly different between the samples with medium to large effect sizes (ϕ = .35–.70). The proximal warning behaviors of pathway, identification, energy burst, and last resort were significantly more frequent among the attackers, and directly communicated threat was significantly less frequent. The distal characteristics of ideological framing, changes in thinking and emotion, and creativity and innovation were more frequent among the attackers, and mental disorder was significantly less frequent. The retrospective results are interpreted in the context of other TRAP-18 research, and in relation to other empirical findings concerning lone actor terrorists. (PsycINFO Database Record (c) 2019 APA, all rights reserved)